I myself am using V3 on 2 forums, it definitely has its issues, but John seems to be a good job phasing them out.
Cons:
Not a good mod if installing a board that has been modded allot already
I need to make a arcade link manually
Some new game errors
Pros:
Promising multi player
Back-wards compatible
Great use of Ajax
Great way to install new games
Great Awards and challenge system
Now I have yet to install IBP, so there could be something I am missing, but if it helps, we are planing on paying the $60 and going branding free