After a couple of days in the Fluent-world I am taking to it as a fish to water.
One of the features that I am tried out and really think will be helpful is the ability to test your mappings. Especially nice is that you in your tests can switch to a in-memory database (with SQLite) so that your test run faster, and without having to setup a database.
I found a good introduction to NHibernate and Fluent NHibernate by the Hibernating Rhino Gabriel Schenker that also introduces mapping testing. Read it here (part 1, 2 and 3).
Love this quote by the way: “if you continue to implement your own data access code you are stealing (money) from your customer”