I have used one for pool shoots with a d2x and a d700. I found that focussing and composing was a big problem as you are looking through a mask, fiddly bit of plastic which moves around, and then the eyepiece of the camera. One major issue was that the bag kept compressing the zoom lens, pushing the front element back with the water pressure ( I think they have something which counteracts this). On the other hand, it is the perfect thing to use if you are on a small budget. I had no issues with leakage but I didn't go down more than 1.5 m. It is a big learning curve. I don't dive, but used a snorkel with weights the second time I tried.... this helped my composition. The other limitations are the length of time your model can stay submerged. On my second try I also used a couple of SB800s on the side of the pool attached to a pocket wizard (in ziplock bags)... this really helped hugely as I was unprepared for the fall off in light as you go under. This is real budget stuff but it means you can do it all for less than €600.
