Yeah, there's lots of debate about app killers. I recommend having one and keeping it around for quick access just in case (Advanced Task Killer will even sit in the notification menu). Sometimes an errant app that is suddenly eating away at your CPU might need to be stopped quickly. Relying on it to shut everything down every half hour or so is pretty pointless, though, so don't rely on it to cure all your battery woes. You can even leave autokill off or keep it on a safe setting.
I do recommend an app like Juice Defender or the one I use, Battery Defender (which I like for its simple interface and light weight). They shut down data services when you don't need it. And in case you have an app that you need to run all the time (i.e. ones that push notifications that you need), you can whitelist those in Battery Defender. And yes, these apps do save battery.