I haven't. I've been "loyal" to EF since the LinqToSql days, though I did use NHibernate heavily about 10 years ago. My main draw is the quality of the tooling and the nice EDMX model designer. The other draw is Linq support for compile-time type-safe queries (which I've noticed are compiled into good SQL with less mangling than I'd expect).
I am guilty of not staying on top of trends outside the MS camp. I does NHibernate now offer parity with EF? I just don't want to write SQL/HQL in strings.
I think it has full linq support now (although could be wrong), but it's had type safe queries for many years now, almost as long as .net has had lambda expressions. It's very much like using EF without linq and just using the .Where syntax. I've used it on some projects that never had any HQL (which is an abomination). There are also a bunch of stuff like future queries that could make it much more performant than EF.
I am guilty of not staying on top of trends outside the MS camp. I does NHibernate now offer parity with EF? I just don't want to write SQL/HQL in strings.