Mobile Demand recently introduced the xTablet T8700.  A rugged tablet pc which works underwater. Engadget reviewed the product including a video using it underwater.  At this time I am unable to determine how deep the T8700 will dive, but hopefully someone from MobileDemand might give us an answer.  Right now it can be used by divers to help log current dives and information while still aboard the dive boat, without fear of getting it wet.