The original Powerbullet forum has loads of useful information. It's the first stop for help on Powerbullet. Generously maintained by Florian Schmitz and the folks at CDBurnerXP.
The Powerbullet Google group is mostly a backup. You can always drop in there if the main forum is down for any reason.
And don't forget Flashcooker where your friendly chef Mark Baird is regularly cooking up tips, resource links and other easily-digestible info.