In the UK it's ridiculous, barely any speed cameras and those that are there are clearly marked (legally have to be). Everyone just slows down for the speed cameras and then start speeding again after.
I've actually heard people say that the above is effective because it makes people slow down where it's important. Or, you know how about people just don't fucken speed in general?
If it were up to me they'd be everywhere, totally unmarked and all revenue from fines would go to charitable causes to rule out the "but they just do it for da money!11" bs - no, they're doing it to stop people speeding and killing someone for fuck's sake.
Stop speeding.