Just spotted the Campus Bible Study Forum when I visited CBS's website to check out some information! And I am now the proud registered user number 23!! Too bad that user registration require moderation, which is actually a good idea for a ministry site like CBS. Thus I shall post my feed back here, since I have not been able to log in and write.
For the Anointed One's sake, please do not use phpBB! phpBB security fixes have been released at least once a month so far this year, and I have seen numerous sites getting defaced due to their lazy admins failing to apply security updates. You might be able to claim that it is "Christian persecution" if your site got owned, but I don't think it is a good idea.
Can't really recommend something that is rock solid either.
FOCUS forum is using PunBB , which also has quite a few security issues this year. Well, nothing is security, as phpBB's project manager has claimed. Just that some is worse than the others :)