I believe Unsolved Mysteries did a segment on this topic several years ago. Sixty Minutes is also going to do a piece on it this evening.

Yeah, it seems hokey, but eerily believable at the same time. It'll proabably never become widespread because insurance won't cover it.

Some dogs (more the scent hounds) can also detect when epileptics have a seizure coming on. Apparently there is distinct change in body chemistry just prior to the seizure that the dog can smell/sense.

Both phenomenums have been scientifically proven. Dogs truly are, our best friends! ;)