Not a lot to say other than, VB just want your money for unfinished products. I got Vbulletin in the 4.# Loved it to begin with because it was the same software that I was used to moderating on another site, started to go down hill for me when I realized how much maintenance was involved with VB, every other week I received an email saying about a "Security Update or Patch" spent most my time in the adminCP or FTP, and that was with under 100 members.
I switched to IPB just to try something new, Now with a site of 12,000+ members I spend a lot more time chatting in the forum rather than keeping it running, Security fixes and patches are every couple of months instead of weeks, as IPB like finishing their products before release. the site is a lot more stable, skins, hooks and apps are easier to install/upgrade and manage.
IPB is the way forward, VB is going in the wrong direction.
I already run 2 IPB sites and have plans for another 3, the ONLY reason I would stop using IPB is if they shutdown.