I use SMF2 for my personal site. It's pretty good (SMF1 was a bit lacking in features, and required complex add-ons to make it an effective forum. SMF2 is a major improvement) and has been stable for me. There's already a nice number of add-ons (or whetever they call them) available for it, too.
I wouldn't switch from phpBB, though. It may not have been the greatest choice, but it hasn't exactly done you wrong either. The pains aren't worth the gains.