At least there is a GUI tool for NHibernate that simplifies mapping files creation and NHibernate queries debugging. NHibernate Query Analyzer is good for the first sight. I did not dig into details yet, but the tool is usable and quite clever. It converts NHibernate queries to SQL queries, provides chooses where possible and maybe could generate source code (there is a option, but I did not try it).
One disadvantage is a lack of a User Guide, but I hope it will appear soon.