NHProf is a great too for profiling a NHibernate application. It is powerful and easy to use.
I used it for a long time, but recently I ran into troubles when I tried to capture DB queries in my newly started web application using NHibernate 3.0.
As many times before I downloaded latest NHibernate release, created a new web application, added a references to NHibernate.dll and all dependencies, added a reference to HibernatingRhinos.Profiler.Appender.dll and put a code, initializing NHProf - HibernatingRhinos.Profiler.Appender.NHibernate.NHibernateProfiler.Initialize(); in Application_Start.
After all that I expected NHPfrof be working smoothly, but all what I got was NHPfor window with no record, but indicating my application is being profiled: