I've seen a few sites I go to change to IPB 3, but there is one problem. It takes a freaking eternity to load on Internet Explorer.
Also, if you put any sort of dependence on ranks or something similar on the rep system, it will not work. I highly recommend leaving the rep system for reputation and not to determine who gets special privileges.
Finally, I think making a forum for bug reporting would be better than having topics like "OMG I CAN'T SEND TEH PMS NOOOOOOOOOOOOOOO" taking over the Noob forum. I can assure you there are many glitches and bugs with IPB 3 that you'll want to take care of quickly.
Good luck with IPB 3, and I hope you guys have better luck with it than others have.