I wear my harness over my vest and a camelbak over the lot. On the camelbak I keep my strobe, knife and gps. I have found that if I need to get free all I have to do is bend forward and the hook collapses into my body and I float back up to the surface. To unhook in a weird position all I have to do is relax and straighten out. Once clear Ijust place my hand over the hook and I can swim clear.
I crashed my boat hard once breaking a few ribs. The post mortem done by my doctor said that I probably would have had more serious injuries had my gear not absorbed most of the punishment. The vest is trashed and now hangs on the wall as a reminder.
In short the most important thing to remember when everything starts to go wrong is to RELAX AND THINK -- Panic kills.
Steve