we just finished an EXTREMELY painful 'upgrade' from JB5.2 to JB6.1 (eap). We had a huge number of issues, and many lingering bugs. I see that 6.2 (eap) was put out a few weeks ago, but i'm on the fence as to if we should upgrade to that one. 1/2 of me says we'll get sacked with a ton of new issues, the other 1/2 says 'they must have fixed a lot of stuff' in 6.2. Does anyone have any experience going to 6.2, how did it go? Quite frankly we were a lot happier (and more stable) on 5.2 eap.
Upgrading from JBoss/EAP5 to AS7/EAP6 will be different as there is a complete reimplementation with lot's of changes between it.
If you have already upgraded to AS7/EAP6.1 there should be no big difference. If you have used some JBoss specific classes there might be some changes