Originally Posted by =X=
It's Androids way of multitasking. It doesn't necessarily mean the app is running on the background it means Android has saved the App state, kind of puts the app to sleep so it does not use CPU, it is however using memory. If the system memory runs low Android will close the app to free up memory, meanwhile still saving the sate. You don't need a task manager to kill the app some Android gurus even argue it's bad to force close an app.
It took me a while to get use to this and after a while one does. My experience is for the most part apps behave properly and you don't have to close apps. The only time I use a task manager to kill an app is when the app is misbehaving.
Agreed. I think there was an issue in an earlier version of Android that was resolved, but the urban legend continues.
If you really need to stop an app, just go to settings -> applications -> the app name -> force stop button