I have a hero2 with the wi-fi backpack. I got the camera new when they came out, but just recently bought the backpack (on clearance for $30 on Amazon). Aside from the 3 second delay, my only complaint is its inability to transmit through anything but air. On the hood of my car my phone won't receive video (but can control it) from inside. I can get 20-30 yards open air though.
It would be a great idea to use it as a shot cam if there was a way to get it to transmit 100-200 yards.