I have the very small Canon ELPH 100 and the WPDC10 housing for it. I have overall been mostly happy with it.
Much of my diving is done in very clear water and in good light, and my results have been good and it has been fun to work with the camera and figure out what I needed to do to get the best shots.
The still images are good at 3.2MP, good enough for checking out on a computer screen and emailing out to friends. But not quite up to full size publication quality.
The movie mode is nice, since it allows me to shoot 30 sec video clips. It is MPEG video, so at times it looks a little jerky, or like things were filmed in slow motion, but the overall effect is still fun to play with.
The main complaint I have with this set up is that you are forced NOT to use the flash. The flash is mounted very close to the axis of the lens, and as a result illuminates all the particles in the water (so it looks like it is snowing in flash photos). I am planning to buy an add on external flash with a slave, but that is probably a year away still, and will make what is now a very small, compact unit much more unwieldy in the water....
The short 2x zoom could be longer as well, but you want to get close to things and shoot wide angle in the water anyway..... Not that the wide angle on this is very wide (about equal to 28 or 35mm lens length in an SLR type camera).
I paid less than $400 for both the camera and the housing, plus an additional $100 for an extra battery pack and a 512Mb SD Media card (it only comes with a 16Mb card, which only gives you about 20 shots {or three video clips}, with the larger card I go over 200 pics {and/or dozens of video clips}). For what I paid, it is a fun toy and I have some nice UW shots. Plus, since I can take it out of the housing and use it on land (it fits in a small pocket), it is very versitile little camera.