We used them a lot. You can check out some of the videos we used them in at our Youtube page:
www.youtube.com/user/eagleforce2073
We had 3 mounting positions. One in the middle of the bot, off to one side and attached to the frame. One closer to the top, attached to the frame. And one just inside the front bumper, giving a nice view of the ball intake with a glimpse of the field.
At Calgames, some teams expressed concerns over using GoPros on bots and advised us not to use ours. Apparently, a couple of teams had issues with their GoPros "frying" during matches. This never happened to us, even after use during 2 regionals and 2 offseason competitions.