Here, in the continued foray into LINQ and the 3.5 (Orca's) release, is an implementation of LINQ over NHibernate.
http://ayende.com/Blog/archive/2007/03/16/Linq-for-NHibernate.aspx
Oren Eini provides a starting point, if not a great example of how LINQ can be expanded to work with data represented in different forms. Hosted up on SourceForge right now in subversion there's also a zip download on his site (NHibernate.Linq.zip (2234082 bytes)).
Now, all I need is LINQ for my keys.... (car keys that is)...