Everyone is nuts with these task killers. First thing you find on every forum is "install a task killer to get better performance and free RAM".
The question is, do task killers really improve your phone's speed and improve battery life?
The answer is NO. Why? Because Android works different than Windows. Do you think that the engineers where morons and released an OS with RAM flaw? Trust me, the OS is very optimized, and whenever android needs more memory, it auto shuts down processes that are not being used.
Android tends to keep apps in memory for faster re-launch, but these apps do not use any resource, so they will not drain your battery.
The more free memory you have on an android phone, "the worse". Why? because android restarts processes. So think about it. You get a Task Killer, and kill an app. The OS restarts that app with time, and the task killer kills it again. Basically this means that it uses up MORE battery. Kill, restart, kill, restart, and so on. Also some apps are not made to be force closed (thats what task killers do..). You may even end up with the app not working properly anymore.
When I got my phone I installed a Task Killer. After I understood how android works, I uninstalled it, and surprise: same battery life and same performance...
The real problem is CPU usage. Sometimes an app goes rogue, and starts to eat a lot of CPU, thus the battery drain. So keep away from task killers, because the more free memory you have, the longer it takes the apps to launch (less free memory = loaded apps = fast app start). You may end up with alarm clock and other apps you don't want killed being killed by the TK, if you won't set it up properly.
Don't forget, Android is made to auto kill tasks when it runs low on memory. The CPU is what's causing the lagg and slowdowns (and Task Killers do not monitor CPU usage...)
I will explain how to get extra standby time out of your phone and what apps to install soon.