I love taking pictures of my swim lesson kids with my waterproof point and shoot camera. It's a great reward for the kiddies and it lets me practice some of my editing skills, since underwater shots require quite a bit of touching up!
Last summer I used to go underwater and look at the screen to try to get the shots I wanted. This was actually pretty frustrating, because it was really a crap shoot as to if I could get a great shot. I mean, taking pictures of 3 and 4 year olds is hard enough... try doing it underwater!
This year I learned to just set the camera on continuous exposure, submerge it pointed at the kids, and hold down the button! Chances are you'll get a good shot! Sure, I'd put more time and effort in if I was hired to take some underwater portraits, but for snapshots, I think these are pretty darn good!
I still haven't figured out a better way to edit underwater shots than picnik. It's just so easy to paint on effects that really make the shots stand out. I use the "eye bright" effect on goggles and on some of the high lights on the water. Then I burn the mid-tones on the water to make it look shiny! Its also fun to paint a blue tint on the water to make the pool look even bluer!