Just jumping on the Taskiller bandwagon. I only ever kill apps when I actually start seeing performance degradation. After killing a couple rogue apps, everything is snappy again.
I'd imagine having something like ATK is a bit like the RAM "freeing" apps on Windows. They spend more cycles unnecessarily purging stuff from memory than the rest of your apps do legitimately idling.
The real question is: is it up to the software authors, the users, or the OS to determine how to properly maintain a responsive system?