I've not had the opportunity to properly test the Contour wet, but I've mounted the camera in it's housing on my mask, and it feels both comfortable and secure. There's a 3mm neoprene square to the rear of the goggle mount which aids stability and obviously cushions the unit against the side of your head. You may have to re-adjust mask straps if wearing a hood though as it may well be an unwelcome pressure point otherwise.
IQ is great under good, natural light, but suffers a little in dimmer conditions, becoming noticeably noisier. I'm using the max settings as standard (64min on a Class 6 8GB card) so if you're planning a two dive day you may want to stock up with a couple of cards (they work out cheaper than a higher capacity) and a spare battery - thankfully it uses a Nokia battery which I've picked up for about £2.50 delivered.
As with any new kit I'll be testing on one of my clubs pool nights just to double check the housing. The dives I've got lined up soon are in pretty poor visibility water, it's the dive in the Sifra Rift where the Contour will show it's real worth!
I can post some pics of the camera mounted if folks are interested? I had to say I feel like one of the Borg with it switched on and the twin laser orientation markers streaming out!