For the people who never look at the NHibernate trunk, since December 2009 a new and improved Linq provider is available.
Using the new Linq provider is pretty simple. It all hangs of a Query() extension method on ISession, so you can do things like the following:
1: from c in session.Query<Customer>() select c
I tried it out for some time and every query I could imagine worked.
Great work!