I migrated both my Joomla and CB from 2.5 to now 3.2. I used Akeeba backup to backup and then reintroduce all my tables. I had a good number of users and data on my old site.
I had some problems with password migration but by resetting them to some easy defaults I made it through to Joomla 3.2 (I'm still in devel more so while I have a lot of, "users" they're test cases so personal security has not been a big problem).
I DO have an interesting technical issue:
1) I can login via the CB Login form (front end) ONE TIME only. If I logout, I can;t login as that user again UNLESS as admin via back-end I change that user's password.
Any ideas?