I really enjoyed "Hibernate: A Developer's Notebook", but mostly just for the style/layout. I read it on a plane sans laptop so i didn't really dig into the exercises. i was looking for a Java ORM and our chief architect had a copy of the book and lent it to me. He hadn't used it himself, but had heard good things. i didn't end up using hibernate in the end because while it seems very powerful if you're building a database from the ground up using it, i couldn't find a way to pull in an existing database schema easily.
I chose ibatis instead because ibator(was abator back then) was happy to oblige in dragging in database tables from an existing schema and generating the ibatis artifacts.
But back to the point... the book seemed like a good introduction, that built a test database/app together throughout. It seemed like a pretty good way to learn. The tone was good, and the style was easy to understand. If you're diving into hibernate i would definitely recommend it.
-Lee