As you probably know there is already a Linq to NHibernate provider available but it’s functionality is rather limited and far from complete.
In the meanwhile a separate project is going on where Steve Strong is building a new provider from scratch based on AST. This provider will give a lot of extra functionalities and features.
Today Steve announced the latest updates on his work and it looks very promising. I cannot wait to start replacing the current provider. Of course, this is all in the trunk, so anyone wanting to play either needs to get the trunk source and build it, or take the much easier option of having Horn do the work. Horn builds the trunk on a daily basis, so look for a package built after around 2300GMT on the 16/12/2009 (the package URL on Horn has the datetime stamp in it, so it's pretty easy to spot).