I purchased a GoPro HD from G7 Motorsports two weeks ago. I haven't been to the track yet with it, but I am pumped to be able to take wide-angle HD in-kart videos this season. This will be a big upgrade over the standard-def GoPro that I used last season.
G7 Motorsports is owned by my good friend Chad Gilsinger. He recently formed the business to do driver coaching, build and prep racecars, and to sell items like GoPro Cameras and Traqmate data acquisition systems. Check it out: http://www.g7motorsports.com/