Some have already mentioned how you can beat speeding cameras by not speeding past them, so I won't reiterate. Other commenters complain about how silly speed limits are. I agree, but let's be practical.
For the time being, we're going to have speed enforcement. The public sea change necessary to eliminate that isn't going to happen any time soon. If we must have nannies running around, wasting time and money, who are making sure all the little kiddies are following playground rules, we might as well have machines doing it. Machines that can't prove our identities in court, and don't doll out points that adversely affect our license status and help insurance companies jack up our premiums.
We've got countermeasures (pick your favorite: Waze and Trapster) against these cameras that are legal in all states (unlike radar detectors), and, if you happen to get caught by one you've missed, your driving privileges aren't put in jeopardy.
tl;dr: less cops, more cameras.