Baronic: Just because you press Home, it doesn't mean an app is running. Supposing a long task is happening e.g. it is searching for all of the MP3s on your SD card. The app developer can choose to
pause this task, or do nothing.
A web browser for example, will intentionally continue the download in the background.
If you're playing a game say chess, and it's your turn, and you press Home, sure the app is still loaded, but there is no processing happening, since it does not have to.
Task killers
kill your battery because when you kill a task, you are forcing the device to run the process of killing a task. If you clear memory, you are using battery power to overwrite the memory. Some services are meant to be loaded always, so when they come back and initialize for the first time (e.g. expanding database to memory) then that will also consume battery power.
Thus a task killer actually causes you to use CPU and battery by both killing and by Android restarting the task.
Instead I would recommend you just go into the app and log out e.g. Facebook. Even then, Facebook and any well-programmed app will use the same push channel as Google does - a website can send a message to Google's Cloud, then it comes down to your Android through the
same channel as Gmail, Google Calendar and whatever else Google will sync! It's not like Facebook is running in the background, checking every 10 minutes with the Facebook server...
Of course, this feature is only available from Android 2.2 onwards, the ability to listen to push messages that ask you to open non-Google apps.
Hmm what about games. Games are held in perpetual pause and can bbe quickly ccontinued and taking up ram so it should still be wasting aaway the battery right