I know a lot of people say it isn't necessary on Android, but I have found it completely is, 1st to kill all the crap ATT loads at start once I reboot, and definitely to kill the Market which bogs down my machine if I don't kill it manually. I also need it to kill graphics apps like Gallery, when doing any work switching between these sorts of apps, otherwise my device slows down so much I consider it frozen. Of course you need to exclude many apps from the task killer, but I am finding the advice that you don't need and shouldn't use a task killer incorrect, at least on the Captivate. Maybe other phones work better but this Captivate can hang if there isn't enough free memory available. I'm using SystemPanel which has a one-click widget to kill stuff.