It's great to see that MSFN is using IPB and I hope this won't change anytime soon. IPB just feels "more natural" to use than vBulletin.
Interestingly vBulletin is not *free* and IPB is!
I'd be interested in reading what you think about comparing vB to IPB.
To me it's a no brainer. IPB is tops. Version 2.0 (Alpha(?)) of IPB is looking even nicer.