I heard (not off the net, but not exactly first-hand, either) that a research group to the Farallons had an inflatable experience, er, unexpected deflation, as a result of a white shark.
This would be somewhere around six or seven years ago, and the sharks were being drawn to the vessels for viewing (at that time, chumming was probably still legal within the Gulf of the Farallons Marine Sanctuary. It isn't anymore. And using towed surfboards will be banned soon.)
Apparently, the shark was doing a good bit of exploration, mouthing everything it could get its teeth on: motors, poles, surfboards, etc. and ended up grazing a tube with its mouth agape. The inflatable (or ex-inflatable, I suppose) beat feet for the mother ship, off loaded passengers (researchers, I think), and was hoisted out of the water.
Only time I've personally heard of this happening.
I *think* there may have been something along the same lines written up in "The Devil's Teeth", a book about research (sort of) at the Farallons. Pretty poor excuse for a book, however; moreso since I know the real story behind the authors experiences.