Bike/Helmet Cameras

So - As alluded to elsewhere - I have had a number of accidents/near misses that were not my fault, and have shown some truly poor driving standards. As I generally cycle alone, a couple of quick questions really:

1) Are bike/helmet cams worth it for capturing this poor driving and reporting it? Has anyone had any success reporting poor driving to the Police? Do they actually make you safer (aware this answer unless it has a bright neon sign saying "Smile you're on Camera" is likely to be no, and even if they did, would still probably be no :D )

2) Following on from the above, if someone was to look for one (even for the sake of feeling a bit safer (even if that is just a feeling)) what recommendations do people have? what functions should I look for, and is there anything out there that could record 7 hours plus of riding? (Its a bit of a minefield and I don't know where to start :D )