They certainly have no problem multiplying. I have a large suburban lot with lots of 'em. They don't bother me except when I hear them running around in my attic.......or digging up my landscaping. Err, on second thought, when I used to have a birdfeeder hanging from a tree, the little bandits would chew the rope so that it crashed to the ground, then eat all the seeds at once!
If I lived in the country, I'd probably have a field day picking them off with my Ruger MkIII .22, but I think that would be highly frowned upon in my neighborhood.
Honestly, their utter stupidity regarding moving cars seems to be the most effective form of population control.
Mauser Werke, Schmidt-Rubin, Remington, Colt, H&K, Weatherby, Browning, Ruger, Marlin, Mossberg, Saiga, S&W, Sig Sauer....a few friends of mine