I'm in the market for a piece of forum software, or a hosted service if the software is better.
I've noticed a trend towards IPB, not sure why exactly though.
I've also noticed vB has released an extremely early beta of a new version, which although looks nice, is lacking in several areas and has some humorous FAQs: http://www.vbulletin.com/faq/ (under Common Installation/Upgrade Issues)
The forum software is for OpenBill, which I'll be relaunching in a new/big way in a couple of months probably. I'm expecting quite a bit of traffic as most software support forums do get a lot of attention.
Other contenders so far are XenForo, IPB, phpBB and Vanilla.
What does everyone like to use/see?