If you've paid any attention to the feral cat problem, you've heard of TNR, which stands for Trap-Neuter-Return. The focus of TNR is to stop the overpopulation of feral cats by sterilizing those that can be successfully trapped. This has been a very effective method--much more effective than killing ferals.
There's also the additional idea of creating cat colonies as places where ferals can safely live and be cared for. What do you think? Are cat colonies the way to go?