It may be against traffic laws, but it's very reasonable that cyclists don't stop at stop signs unless traffic is heavy (or a car is already going through). Remember, the lost momentum from stopping a bike comes from the biker's legs and not from an easy press on the gas pedal.
The real solution to this problem is not simply making it illegal for bikers to not stop at stop signs, but to make better trails/paths/roads for cyclists that remove all but the most necessary stop lights and signs. Bryant St's as a bike boulevard has gone more than halfway there, but more can (and should be done).
If you love to drive your car around and hate cyclists, try riding a bike around and see what it's like when you get cut off by a car, or have a smog-test-failing truck just ahead of you polluting your lungs. Your heart and legs (not to mention waistline) will thank you.