I can't answer with 100% certainty, but I can try from my experience...
1) Yes, you need to use the MySQL driver from the install or newer - we're using mysql-connector-java-3.1.12-bin.jar without problems. The earlier driver we had been using broke stuff. ;-)
2) I think JBCS M4 installed version can't run on GA. I think even M5 installed version can't. I'm using a compliled version from CVS HEAD on GA and it works fine. Originally we used M5 on CR2.
3) I don't use jBPM, so can't help there.
In regard to upgrading... I'm pretty sure you'll have to blow away the db for M4 to use M5 as the data structures aren't compatible. So if you've got messages in the db you want, I guess you'll need to export them somehow... I think there was a post about this.
There are even some differences in M5 and HEAD on how the body ids work so older messages break - although I was able to fix this with a db script.
I'm hoping there aren't too many more changes to the data structures so I don't have to rework things when 1.0 comes out. ;-) That's the price you pay for early adoption I guess!
Hope that helps...
So I guess this means its back to the drawing board then for us and figure out what components we need to drop.
Oh yeah, Elmo, this question should probably have been posted in the JBCS User forum:
Not sure if you knew about that forum or not.
No I'm not aware of this forum. Thanks. This helps a lot :).