Guys, any update on running NHibernate in a medium-trust environment? Lately I'm experiencing more and more webhosters moving to medium trust by default and it is causing much trouble.

Some times ago, a Jira issue was created for this, but it is closed with 'won't fix'.

No news on this unfortunately. What you can try is build a version of NHibernate with IdentityHashCodeProvider implementation replaced with a C# one. This will not be equivalent, but it should work, just run tests to make sure nothing fails.