If you're using NHibernate as your O/R Mapping engine and want to include a sophosticated clustered object cache into your project, you should consider using NCache. NCache is a clustered object cache for .NET.

NCache helps you boost your application performance by reducing the number of expensive trips to the database. NCache works in both single-server and clustered multi-server configurations.

Download a trial today from http://www.alachisoft.com.

How exactly does it integrate with NHibernate?

It integrates as easily as the BantamTech plugin, and provides replicated caching across clustered servers (among other configurations).

<add key="hibernate.cache.provider_class" value="NHibernate.Caches.NCache.NCacheProvider, NHibernate.Caches.NCache" />

Looks expensive. You providing a discount to NHibernate users that want the clustered edition?