I'd just like to add guys, we used to use ikonboard, but with a lot of traffic it became very unstable. The forums used to crash almost daily, and there wasn't the support like you get with infopop. They might have got their act together, but my site, personally I wouldnt use ikonboard.
Vbulletin I have never used on the other hand.
BUT, I also agree with lance, UBB is poorly written, the last few versions I have been having a lot of problems, corrupt member files, search files etc etc, but the support is bloody good.
Tough decision!
