Hibernate version:
3.2.6ga

Mapping documents:
...
<class name="com.ext.portal.inventory.model.impl.ProductImpl" table="Product">
<cache usage="read-write" />
<id name="productId" type="long">
<generator class="assigned" />
</id>
<property name="companyId" type="com.liferay.util.dao.hibernate.LongType" />
<property name="groupId" type="com.liferay.util.dao.hibernate.LongType" />
<property name="userId" type="com.liferay.util.dao.hibernate.LongType" />
<property name="createDate" />
<property name="modifiedDate" />
<property name="name" type="com.liferay.util.dao.hibernate.StringType" />
<property name="description" type="com.liferay.util.dao.hibernate.StringType" />
<property name="imageId" type="com.liferay.util.dao.hibernate.LongType" />
<property name="url" type="com.liferay.util.dao.hibernate.StringType" />
<property name="properties" type="com.liferay.util.dao.hibernate.StringType" />
<many-to-one name="type" class="com.ext.portal.inventory.model.impl.ProductTypeImpl" column="typeId" not-null="true" not-found="ignore" />
<many-to-one name="model" class="com.ext.portal.inventory.model.impl.ModelImpl" column="modelId" not-null="true" not-found="ignore" />
<property name="sku" type="com.liferay.util.dao.hibernate.StringType" />
<property name="discontinued" type="com.liferay.util.dao.hibernate.BooleanType" />
<set name="costs" inverse="true">
<key column="productId" not-null="true" />
<one-to-many class="com.ext.portal.inventory.model.impl.CostImpl" />
</set>
<set name="prices" inverse="true">
<key column="productId" not-null="true" />
<one-to-many class="com.ext.portal.inventory.model.impl.PriceImpl" />
</set>
<set name="features" table="Features_Products" inverse="true">
<key column="productId" />
<many-to-many column="featureId" class="com.ext.portal.inventory.model.impl.FeatureImpl" />
</set>
<set name="offers" table="Offers_Products" inverse="true">
<key column="productId" />
<many-to-many column="offerId" class="com.ext.portal.inventory.model.impl.OfferImpl" />
</set>
</class>
...

Code between sessionFactory.openSession() and session.close():
For list
DetachedCriteria dc = DetachedCriteria.forClass(com.ext.portal.inventory.model.impl.ProductImpl.class, "Product");
Criteria c = dc.getExecutableCriteria(session));
c.list();

For count
DetachedCriteria dc = DetachedCriteria.forClass(com.ext.portal.inventory.model.impl.ProductImpl.class, "Product");
dc.setProjection(Projections.rowCount());
Criteria c = dc.getExecutableCriteria(session));
Iterator itr = c.list().iterator();
if (resultsItr.hasNext())
return ((Number) resultsItr.next()).intValue();

Name and version of the database you are using:
MySQL (latest)

The generated SQL (show_sql=true):
For list
Hibernate: select this_.productId as productId111_4_, this_.companyId as companyId111_4_, this_.groupId as groupId111_4_, this_.userId as userId111_4_, this_.createDate as createDate111_4_, this_.modifiedDate as modified6_111_4_, this_.name as name111_4_, this_.description as descript8_111_4_, this_.imageId as imageId111_4_, this_.url as url111_4_, this_.properties as properties111_4_, this_.typeId as typeId111_4_, this_.modelId as modelId111_4_, this_.sku as sku111_4_, this_.discontinued as discont15_111_4_, producttyp2_.typeId as typeId114_0_, producttyp2_.companyId as companyId114_0_, producttyp2_.groupId as groupId114_0_, producttyp2_.userId as userId114_0_, producttyp2_.createDate as createDate114_0_, producttyp2_.modifiedDate as modified6_114_0_, producttyp2_.name as name114_0_, producttyp2_.description as descript8_114_0_, producttyp2_.imageId as imageId114_0_, producttyp2_.url as url114_0_, producttyp2_.properties as properties114_0_, producttyp2_.parentTypeId as parentT12_114_0_, producttyp3_.typeId as typeId114_1_, producttyp3_.companyId as companyId114_1_, producttyp3_.groupId as groupId114_1_, producttyp3_.userId as userId114_1_, producttyp3_.createDate as createDate114_1_, producttyp3_.modifiedDate as modified6_114_1_, producttyp3_.name as name114_1_, producttyp3_.description as descript8_114_1_, producttyp3_.imageId as imageId114_1_, producttyp3_.url as url114_1_, producttyp3_.properties as properties114_1_, producttyp3_.parentTypeId as parentT12_114_1_, modelimpl4_.modelId as modelId110_2_, modelimpl4_.companyId as companyId110_2_, modelimpl4_.groupId as groupId110_2_, modelimpl4_.userId as userId110_2_, modelimpl4_.createDate as createDate110_2_, modelimpl4_.modifiedDate as modified6_110_2_, modelimpl4_.name as name110_2_, modelimpl4_.description as descript8_110_2_, modelimpl4_.imageId as imageId110_2_, modelimpl4_.url as url110_2_, modelimpl4_.properties as properties110_2_, modelimpl4_.makeId as makeId110_2_, modelimpl4_.discontinued as discont13_110_2_, makeimpl5_.makeId as makeId109_3_, makeimpl5_.companyId as companyId109_3_, makeimpl5_.groupId as groupId109_3_, makeimpl5_.userId as userId109_3_, makeimpl5_.createDate as createDate109_3_, makeimpl5_.modifiedDate as modified6_109_3_, makeimpl5_.name as name109_3_, makeimpl5_.description as descript8_109_3_, makeimpl5_.imageId as imageId109_3_, makeimpl5_.url as url109_3_, makeimpl5_.properties as properties109_3_, makeimpl5_.manufacturerId as manufac12_109_3_ from Product this_ inner join ProductType producttyp2_ on this_.typeId=producttyp2_.typeId left outer join ProductType producttyp3_ on producttyp2_.parentTypeId=producttyp3_.typeId inner join Model modelimpl4_ on this_.modelId=modelimpl4_.modelId left outer join Make makeimpl5_ on modelimpl4_.makeId=makeimpl5_.makeId where ((((((this_.companyId=? and 1) and 1) and 1) and 1) and 1) and 1) order by this_.name asc limit ?

For count
Hibernate: select count(*) as y0_ from Product this_ where ((((((this_.companyId=? and 1) and 1) and 1) and 1) and 1) and 1) order by this_.name asc

Debug level Hibernate log excerpt:
For list
15:09:19,823 DEBUG [SessionImpl:220] opened session at timestamp: 4981257665835008
15:09:19,855 DEBUG [AbstractBatcher:366] about to open PreparedStatement (open PreparedStatements: 0, globally: 0)
15:09:19,858 DEBUG [ConnectionManager:421] opening JDBC connection
15:09:19,860 DEBUG [SQL:401] select this_.productId as productId111_4_, this_.companyId as companyId111_4_, this_.groupId as groupId111_4_, this_.userId as userId111_4_, this_.createDate as createDate111_4_, this_.modifiedDate as modified6_111_4_, this_.name as name111_4_, this_.description as descript8_111_4_, this_.imageId as imageId111_4_, this_.url as url111_4_, this_.properties as properties111_4_, this_.typeId as typeId111_4_, this_.modelId as modelId111_4_, this_.sku as sku111_4_, this_.discontinued as discont15_111_4_, producttyp2_.typeId as typeId114_0_, producttyp2_.companyId as companyId114_0_, producttyp2_.groupId as groupId114_0_, producttyp2_.userId as userId114_0_, producttyp2_.createDate as createDate114_0_, producttyp2_.modifiedDate as modified6_114_0_, producttyp2_.name as name114_0_, producttyp2_.description as descript8_114_0_, producttyp2_.imageId as imageId114_0_, producttyp2_.url as url114_0_, producttyp2_.properties as properties114_0_, producttyp2_.parentTypeId as parentT12_114_0_, producttyp3_.typeId as typeId114_1_, producttyp3_.companyId as companyId114_1_, producttyp3_.groupId as groupId114_1_, producttyp3_.userId as userId114_1_, producttyp3_.createDate as createDate114_1_, producttyp3_.modifiedDate as modified6_114_1_, producttyp3_.name as name114_1_, producttyp3_.description as descript8_114_1_, producttyp3_.imageId as imageId114_1_, producttyp3_.url as url114_1_, producttyp3_.properties as properties114_1_, producttyp3_.parentTypeId as parentT12_114_1_, modelimpl4_.modelId as modelId110_2_, modelimpl4_.companyId as companyId110_2_, modelimpl4_.groupId as groupId110_2_, modelimpl4_.userId as userId110_2_, modelimpl4_.createDate as createDate110_2_, modelimpl4_.modifiedDate as modified6_110_2_, modelimpl4_.name as name110_2_, modelimpl4_.description as descript8_110_2_, modelimpl4_.imageId as imageId110_2_, modelimpl4_.url as url110_2_, modelimpl4_.properties as properties110_2_, modelimpl4_.makeId as makeId110_2_, modelimpl4_.discontinued as discont13_110_2_, makeimpl5_.makeId as makeId109_3_, makeimpl5_.companyId as companyId109_3_, makeimpl5_.groupId as groupId109_3_, makeimpl5_.userId as userId109_3_, makeimpl5_.createDate as createDate109_3_, makeimpl5_.modifiedDate as modified6_109_3_, makeimpl5_.name as name109_3_, makeimpl5_.description as descript8_109_3_, makeimpl5_.imageId as imageId109_3_, makeimpl5_.url as url109_3_, makeimpl5_.properties as properties109_3_, makeimpl5_.manufacturerId as manufac12_109_3_ from Product this_ inner join ProductType producttyp2_ on this_.typeId=producttyp2_.typeId left outer join ProductType producttyp3_ on producttyp2_.parentTypeId=producttyp3_.typeId inner join Model modelimpl4_ on this_.modelId=modelimpl4_.modelId left outer join Make makeimpl5_ on modelimpl4_.makeId=makeimpl5_.makeId where ((((((this_.companyId=? and 1) and 1) and 1) and 1) and 1) and 1) order by this_.name asc limit ?
15:09:19,870 DEBUG [AbstractBatcher:382] about to open ResultSet (open ResultSets: 0, globally: 0)
15:09:19,871 DEBUG [AbstractBatcher:389] about to close ResultSet (open ResultSets: 1, globally: 1)
15:09:19,872 DEBUG [AbstractBatcher:374] about to close PreparedStatement (open PreparedStatements: 1, globally: 1)
15:09:19,874 DEBUG [StatefulPersistenceContext:837] initializing non-lazy collections
15:09:19,875 DEBUG [ConnectionManager:302] transaction completed on session with on_close connection release mode; be sure to close the session to release JDBC resources!
15:09:19,878 DEBUG [ConnectionManager:441] releasing JDBC connection [ (open PreparedStatements: 0, globally: 0) (open ResultSets: 0, globally: 0)]
15:09:19,883 DEBUG [ConnectionManager:302] transaction completed on session with on_close connection release mode; be sure to close the session to release JDBC resources!

For count
15:09:19,898 DEBUG [SessionImpl:220] opened session at timestamp: 4981257666142208
15:09:19,901 DEBUG [AbstractBatcher:366] about to open PreparedStatement (open PreparedStatements: 0, globally: 0)
15:09:19,903 DEBUG [ConnectionManager:421] opening JDBC connection
15:09:19,906 DEBUG [SQL:401] select count(*) as y0_ from Product this_ where ((((((this_.companyId=? and 1) and 1) and 1) and 1) and 1) and 1) order by this_.name asc
15:09:19,908 DEBUG [AbstractBatcher:382] about to open ResultSet (open ResultSets: 0, globally: 0)
15:09:19,910 DEBUG [Loader:1173] result row:
15:09:19,911 DEBUG [AbstractBatcher:389] about to close ResultSet (open ResultSets: 1, globally: 1)
15:09:19,912 DEBUG [AbstractBatcher:374] about to close PreparedStatement (open PreparedStatements: 1, globally: 1)
15:09:19,917 DEBUG [StatefulPersistenceContext:837] initializing non-lazy collections
15:09:19,920 DEBUG [ConnectionManager:302] transaction completed on session with on_close connection release mode; be sure to close the session to release JDBC resources!
15:09:19,922 DEBUG [ConnectionManager:441] releasing JDBC connection [ (open PreparedStatements: 0, globally: 0) (open ResultSets: 0, globally: 0)]
15:09:19,923 DEBUG [ConnectionManager:302] transaction completed on session with on_close connection release mode; be sure to close the session to release JDBC resources!

Results:
When I run the count query (same query but with a count projection), then I get the result "1" back, indicating that the query found 1 row in the db (which is correct in this case).
However, when I run the query as a normal list() get, then it returns an empty List.
Could it have something to do with the "not-null" attribute in the "many-to-one" tags of the Product mapping? If, for instance "typeId" equals 0 (no type), will this cause the query to fail for this row?

Thanks in advance.

Right after I typed the post, I tried removing the not-null="true" attributes of the many-to-one tags. This solved my problem.
:)