I used a Canon AW-DC30 enclosure for an SD400 on our recent Caribbean trip, and must say it was pretty frustrating. The main issue is that you can't see a friggen thing in the LCD underwater, and you can't use the optical viewfinder at all. So, you have to frame the pics by "feel". Also, the slow reaction and weak flash of the cheap "pocket digicams" don't help the situation a bit.
Basically the same elements that drove me to buy a D200 for on-land pics were even worse underwater!
Here are a couple that I got --
On the plus side, the housing does work fabulously for above-surface shots while swimming, snorkeling, in the rain, etc.