Thanks for your replies. I have to agree I see a lot better performance without using any auto task killer. However, I use GoLauncher, and there's a tab to see all running programs, and you can click and stop all running programs. Is that also something I shouldn't bother doing?
On a side note; does anyone use some kind of cache clearing program? One that deletes cache from all programs? Or is that also not suggested?
If you're killing tasks that start up by themselves then you are wasting your time and battery power and slowing down your phone. I would only kill an app in the rare circumstance that it is frozen or otherwise acting strangely. If an app has an "Exit" or "Quit" button, it's not a bad idea to use it--especially Google Navigation's "Exit" button. However, for almost all apps you can just press your home button. Some people insist that they press the back arrow to back out of every app, but I find this to be completely unnecessary (at least for the apps I use).
I don't clear caches unless there is a specific problem with an app. Otherwise, what's the point? The cache will just have to be rebuilt--slowing your phone and using battery power in the process.
Really, just use your phone. Don't worry about all of this task killing and cache-clearing stuff. The phone handles this on it's own really well without any extra apps or input from you. Here's the maintenance that I do on my phone:
1) once every 2 months run the battery all the way down and charge it all the way up nonstop to calibrate battery meter
2) once every month dial *22899 (from a place about equidistant from work & home--not sure if it matters though) and wait for it to hang up
3) clear cache and kill an app only when there's a specific problem with an app
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EDIT: I focus on the privileges that apps require and whether or not they run on boot. If an app wants unneeded permissions, I uninstall it and find an alternative. If an app runs on boot for no reason, I do the same: rate it poorly, leave a comment in the market, uninstall it, find something better.
Also, I try to run lean. For example, I don't need a widget to tell me my battery percentage. Why waste battery power with that function? If you'd really like a widget that will do that then I support your decision, but I recommend that you find one that is lightweight (doesn't use a lot of resources). My philosophy is to cut down on the bells and whistles and focus on having a fast phone with long battery life while still having all of the functionality that I really want. I guess I'm a conservative guy. Sure, I'll install fun widgets, etc. once in a while but as soon as I get bored of them I uninstall.
No auto task killers, no antivirus, no BS.