Entity Framework vs NHibernate

NHibernate vs EntityFramework – Experience From the Real World

This is a really great article, unbiased well developed review between EF4 & NHibernate.

NHibernate and Entity Framework essentials using a Model First approach

This is brief sample of implementation with comparison

BTW, the conclusion is

1. If no special reason, stick to ADO.Net with DataSet
2. If use only MS DB(MSSQL) and the project is relatively simple, EF can be an easy choice.
3. If the project is complex & teams are ready for steep learning curve, Fluent NHibernate is a king.