Matt Raible has some interesting feedbacks on the migration.
http://raibledesigns.com/rd/entry/upgrading_hibernate_to_3_4

There does not seem to be a readme file in the dist anymore. It probably would be nice to tell people to use the JBoss Maven repo and some words about the distro structure.

The documentation on the website still is for Hibernate 3.2.2 (http://www.hibernate.org/5.html)

http://opensource.atlassian.com/projects/hibernate/browse/EJB-382 is pretty bad, we should release a 3.4.1 somewhat soon (as in before AS 5 GA).

Not sure where his javassist to cglib migration problem come from, I could not even find the documentation he refers to so he was better than me :)

Lost of people are bitten by the slf4j implementation drop issue: unless you drop an slf4j impl, you get nasty CNFE. I wonder if we could make that easier for users.