Task killers in Android rarely do any device any favours. The way Android manages background apps is to basically suspend their state and keep that in the background, so when you switch back, it resumes from wherever you were before. In Android, background apps do not affect your battery life or the performance of the device.

At best, task killers do nothing. In some circumstances, like if you use an auto-kill feature, task killers can use up the CPU in the background monitoring and killing apps.

The GetJar market should have an app called Watchdog available. Rather than monitoring RAM usage (which is damn near useless), it monitors CPU usage. You can set it up so that if there's an app using up your CPU more than it should, it'll let you know and ask you if you want to kill that app.

It's a similar situation to when Microsoft changed memory usage in Windows in... I think it was Vista. So in Vista onwards, if your RAM is full or near full, it's a good thing, because Windows does something called precaching on programs. It works out what programs you use the most and so are most likely to launch, and precaches them so they open more quickly.

So these days, RAM tends to be used a little differently to how it was even five years ago.


Might also be worth noting that, depending on how an app has been written, using the Back button won't necessarily exit it. It generally does, but again, it depends on the developer.