This Kind of Makes Sense: A Case FOR Task Killing

Download the System Panel app and see the resources those programs use when not actually in use. It really doesn't matter that they're "running," because Android doesn't give them any resources.

In fact, System Panel will help you see which apps really ARE using cpu resources, and consequently battery power.
 
My own experience would tend to agree with those that suggest these app killers do more harm than good. I installed ATK and set it up to only kill tasks when I manually told it to. I didn't even let it run in the background. I was sure to never kill a task that even remotely looked like it was used by the system. I am a twenty year veteran software developer, so I consider myself a touch more than a newb.

The result was that not only did my battery seem to be exactly the same. I found that apps would force quit on a regular basis. I even tried doing nothing but review the apps with ATK, without killing any but somehow things seemed to be unstable. I read a number of articles, and after a week of testing I uninstalled ATK.

Since then my EVO has had no issues despite heavy daily use. My experience is purely anecdotal, but for me task killers on the Android seem to be a waste of resources.