Never understand why everyone is so quick to tell other people they are using their device wrong. This is Android, not Apple. OP asked how to use a feature of a task killer, not for anyone to tell him if he should or shouldn't. He's already made his choice so might as well respect that. I understand how Android runs Linux kernel and apparently knows how to allocate memory and resources better than other OS's. I'm no expert, but I have a little knowledge. I never have went out of my way to kill a task with my Incredible, and it runs great. However, when I was using the Eris, if I was app-jumping and multi-tasking lots, I would notice a performance increase in how I used my device if I killed some apps. How I used my device. My device.
OP, since you asked about the auto-kill and not for me to shove my opinion down your throat, are you sure you have the widget on your home screen and not a shortcut to the program itself?