I've met the Google camera on the road a couple of times, once locally and once in Europe. Car doesn't appear on street view though.
I'm told the view is only updated if there is a substantial change since the previous images, ie a new junction, sign or building. Therefore one image could be taken heading in one direction and a more recent image from the opposite direction. The two are then merged to make a 360°
This would explain why cars seem to appear and disappear.
