As someone who does all the diving (SCUBA and Sky diving) I’m around GoPro’s all the time. I’ve had a Hero 2 for over a year and use it on almost every dive (over 100 in the last year alone) with no issues.
I’ve heard lots of complaints so far about the Hero 3 from fellow skydivers and the advice has been to steer clear of it so I’m still shooting with my Hero 2 and looking at a 2nd one for my wife as well.