I am an active member on one, although there is a planned change in the pipeline according to Transworld who run the forum.
My forum started out as phpBB2 and I didn't have a choice because I was using a free forum hosting site (which has since gone off-line). When I moved my forums to a for-pay host, I remained on phpBB2 for the reasons that others have mentioned, namely the number of mods that were installed in my phpBB2 system. But, a few month ago I finally bit the bullet and updated to phpBB3. The migration was mostly painless, but it did take about a week to get the minor issues worked out, but my users are much happier with the new system. I am currently on version 3.0.9, have yet to update to 3.0.10, waiting to see what experience other have with the update.
Well, when you go to phpbb and register for a forum, it is phpbb2. And then you have to upgrade to 3 and wait 2 days, and then when you do that it makes your forum name really long- like allofthischat.jeltz3.myfastforum.org, the name in phpbb2 is shorter.
