About 19 years ago, we lived in Long Beach. Our neighborhood became infested with roof rats. You could see them running on the utility poles and wires. We also had a gopher problem. Every morning I'd get up, grab a shovel and dispose of all the dead varmints, courtesy of my two Russian Blue cats. Finally the county came out and put up poison bait. It solved the problem. You know it's a problem when a neighborhood full of cats can't get rid of them.
Then there was the mouse explosion up here in the desert. The calico cat would dive into the kitchen pantry closet, and went after them. She'd kick canned goods out with her hind legs. It was pretty funny seeing cans come shooting out of the cabinet :)
Saw a bumper sticker awhile back that said.."Cats..the other white meat"
A co-worker of mine gave away his two cats because he was never home and he thought that is was unfair to them. A very short time later, one night at around 10 pm, he heard strange noises in his apartment -- turned out to be mice. He panicked and called an exterminator to deal with them. He paid plenty got sn exterminator to come in the middle of the night and he admitted that he didn't have the problem until the cats were gone.