Personally I would be surprised if it took longer than the end of the year for there to be a notable percentage of USB 3.0 devices entering the market. Backwords compatibility will make it easy for MP3 players to waste time getting to it, but anyone that has seen thier friend transfer thier music collection onto a 4Gb+ USB 3.0 Mp3 player will immediatly want to swap thiers out. And seriously, who the hell wants to wait 45 min to fill a 16Gb usb stick. Um, a couple minutes - yes please.
These are just the first most obvious things to hit the market but video recorders, editors and camera's will want nothing to do with USB 2.0 with 3.0 out there. Full streaming raw 1080p with 7.1 audio via usb, again, yes please.
Honestly, how long do you think it will take. The wave of motherboards hit this summer with a stream of devices soon to follow. If the HDTV and HDReciever market don't soon follow I'd be shocked. I mean how else are you going to transfer those 3D home videos from your new 3D camcorder.