Over at Lifehacker, they’ve written up a very thorough guide to why you shouldn’t bother using Task Killer applications on your Android phone—because they really don’t do any good.
We’ve done a lot of research here at How-To Geek on this topic, and all of the research concurs with everything Lifehacker has written. Even if you kill applications, or setup a rule to automatically kill applications, they can simply respawn any time they want because Android allows applications to bind to events, or even a timer event. Badly written applications should simply be uninstalled, not tamed.
And, of course, you can always force kill applications easily without a task manager.