I have seen lots of .NET architect speak highly about NHibernate which I agree that is a great framework but I think that as it was ported from java they did not take the .NET advantages in consideration. I have tried for a while to use gentle.net framework which I found to be more of what I expected from a .NET framework as it uses attributes as it's mapping mechanism and by that you get in my opinion a better experience as a programmer.
“Gentle.NET is a CLS-compliant, database independent object persistence framework. It has an extensive feature set, excellent performance, and reasonably complete docs. It features automatic SQL generation, object construction/caching/uniquing, validation, bindable list support, relation management, transactions, and much more. Oracle, PostgreSQL, MySQL, Firebird/InterBase, MS SQL Server (incl. CE), MS Access, SQLite, Sybase, and Sybase ASA are supported. It includes a NAnt build file as well as VS.NET project files for building under Windows. Mono 1.1.4 and higher is fully supported.”