I bought a P150 with the Sony underwater housing recently, and took it to a recent trip to egypt in the red sea. I have taken it on more than a dozen snorkeling trips and I am very happy with the results. With the housing it feels great and easy to use underwater. I did my shoot in program mode, with forced flash and increased flash intensity, and with added saturation and sharpness. To be honest about 2/3 of my shots were good for the bin, but as this is my first underwater photography experience, I think it is due to me and the difficulty of shooting underwater rather than the camera. I find the LCD is quite hard to use underwater, so most of the time I just estimated how I should positioned the camera; when scuba diving instead of snorkeling, it is probably easier, and the LCD might be more useful.
I include a few resized pictures I have taken, both the original and a photoshoped version.