Not really, it's a painful process migrating. You'll need to export and re-import your CB users though and for that I recommend CB Juice.

I use direct database manipulation, but I don't really recommend that.

I believe jUpgrade supports CB though and should allow for pretty painless migration. You may need to go through and re-set some of the access permissions as the ACL changed quite a bit.

You'll need to contact them about that, sorry. Like I said migration is a nightmare and there's no getting around data loss, you will lose some data. I've always installed CB then directly copied over my CB database tables. Once done I exported from _users, used REGEX to mass modify the export file, re-imported my users. Now that the users exist I manually exported and re-imported the usergroups mapping database table. It's a lot of manual database work, but has zero user loss. I don't recommend this approach unless you've very good experience with database usage otherwise please use migration tools and CB Juice.

As long as user_ids remain the same you can quite literally copy and paste your CB, CBSubs, and GJ database tables. jUpgrade I hear does pretty well moving _users and their ACL while keeping user_id so you may want to move the users first then database export and database import your CB, GJ, and CBSubs tables.