There's an estimated two million of them in use on UK roads. So you're likely to be on someone's anyway. You can be prosecuted for reckless/dangerous/without due care on footage from someone else's camera. I think it's a good thing as it's going to put the blame where it belongs instead of spreading the cost around.
Someone cuts you up, weaves around the road, overtakes in a bad spot, blasts past well over the limit etc. etc. and you just send in the footage. In other words, drive like a c**t and you're more likely than ever to get nicked.