I tried it once when it was first introduced with iOS 5, with my iPhone 4, and it was sooooo sloooowwww I turned it off and never used it again. However, I just tried it with my 5, and it's actually usably fast. Not quite as fast as USB, but fast enough that I'm willing to use it now! So if extreme slowness turned you off of the idea of Wifi sync, give it another try. You'll be pleasantly surprised.