I used to have an ATC too, and I also got fed up of the vibration – no matter how i tried to affix it to my helmet, it always suffered terribly from vibration. I found the best way to use it was with the handlebar mount, as it was much more secure, but didn’t give as good a view point.
In the end, as I was going to use it for both MTB and skiing, I bit the bullet and bought myself a GoPro, and the mounting system is miles better. The camera screws into the mounts, and most of the fixed mounts screw onto things too – frame, seatpost etc. I can’t really comment much on the helmet mounting, as I haven’t used it much on my MTB – some footage on helmet here http://vimeo.com/19516530 – about 1m50s in.
Other mounting options in this little vid: http://vimeo.com/18991303