I have been using GoPro HD cameras since these were released and have had no problems. Some of the people I know have been using Contour HD. IMHO, GoPro HD has better video quality (colors are more saturated). Also the 170 degree wide angle setting when recording at 720p gives a better perspective of speed, again my opinion.

It is indeed bulkier when mounted on a helmet but you can mount it on the handlebar, chest, etc., if this bothers you. The controls do indeed take getting used to but after a while you get accustomed to it.

EDIT: Here is a sample video from my 2 GoPro cameras (one mounted in the drops and the other one facing to the rear on the seatpost):