I only used it the one week in Kona, and I have no extra stuff for it, just the stock features, but I still got some good underwater video, especially of the manta ray night dive. I made my own lanyard for it and tied it off to my BC. (A tool lanyard from work heh) I will get some sorta of flat lens/color correction for the next time I go diving, hopefully this summer. The video came out pretty good with the basic case, but the underwater pictures had some real blur distortion.
*edit* I was generally not running the camera the entire dive. I would leave it switched on, but turn on/off video as needed and take pictures as needed. The only dive I left it recording the entire dive was the manta ray dive which was 30+ minutes of footage. Don't remember exactly how much battery was left after.
One thing to watch for when diving; I did this while doing some snorkeling with porpoise between dives and missed some great video of them 10 feet away from me. When you turn on the camera, if you hold down the power button a second to long it will switch you from video to camera mode. CHECK every time. That was the one time I didn't check (it happened several times) and it bit me and cost me some great footage. Was rushing trying to get into the water to snorkel with them. I posted a short video clip I took in the thread about the Hero2 flat lens case of the night dive. It came out pretty good, considering my limitations.