We're trying to do our part... catching neighborhood cats and getting them spay/neuter. A vet has a special one weekend every other month for $45 (cats), $70 dogs.
Some people will feed the cats and let them breed freely. There were 2-3 when we moved in years ago. It was getting a little crazy with 10-12 cats in our cul-de-sac last year and the numbers were growing. Since no one was officially claming the cats, another neighbor and I would live catch them and get them "fixed". I think every cat has been taken care of on our street.
Every now and then a new one will show up.