Hi.
Well, the process is not so bad at all.
To backup your database first is always a good idea.
What i tested was this:
Installed under joomla 1.0.3 was a version of CBE with CBE included, selfmade function tabs and normal added tabs containing fields.
Backupd DB, uninstalled CBE, installed CB-RC2.
All Data was still there, all fields with their values were still there and useable, same goes for the normal added tabs containing fields.
What was not usable were the functional tabs CBE brings with it. Also some naming of Tabs with _UE_ had to be done, but that belongs to my own changes on language files which can be edited.
Viewing the database, there are now some leftover tables like _mambome_gbook, but to clean up them is easy. Even so it does cost time, but it is better than starting from scratch and doing some database vlaue injections afterwards.
Greets
Phil.