I just purchased a license for vBulletin 4, and updated Resin/Quercus to 4.0.7, and for the most part it appears to be working OK. I'm getting errors when trying to add an avatar, and when trying to edit my signature after having already added my signature (I was able to add it without error).

I hadn't seen the update to Quercus until after I purchased the new vBulleting license, or I would have just reinstalled phpBB 3.0.7-PL1 after that botched upgrade. Oh well, this is actually a really nice forum, with a lot more features and functionality than phpBB 3. Now I'll be hounding Caucho with errors for a few months (or more) until they get them all fixed, but that's OK, because it creates a better product for everyone.