I seem to remember seeing somewhere a while ago that RIBnet admin were considering migrating to Invision Power Boards from the vBulletin software.
Don't do it!!
I am on the admin/mod team for another forum and we have just upgraded to IPB v 3.2.2 after a period to 'wait for the bugs in the new version to be ironed out'.
They still have a way to go - and every new version of IPB gets worse. Random problems with different browsers, screen layout screwed up from the previous version of IPB, and as usual they lost all the custom stuff but that is normal anyway.
What used to be a nice quick and efficient forum a few versions ago, is now much slower and something that gets screwed up every time there is an upgrade and the admin team have to spend ages fixing everything again.
Just thought I would forewarn you - if it is still a possibility, think about it pretty hard as it will not be without problems!