I'm playing around with vBulletin.
For those of you who are not forum junkies, vBulletin is by far the best forum software out there. I probably should have upgraded to it last time.
For now, I'm looking at how a test migration would go.
vBulletin has a FAR superior search feature, a ton of admin functionality that we lack now (like merging threads), and just better all around reliability. We've had off and on problems with link management on this forum (some pop up a new window, others just go to a new page in the forum window), some strange log-in problems for some users, etc...
Anyway, I'll keep you posted on how it goes.