Apparently something new is coming in later builds of BlackBerry 7.1
Its being called Application resource monitor, and it does just that. It monitors applications and if an application is using too many system resources it will kill that background process, theoretically saving battery life.
I actually saw this Application Resource Monitor on my PlayBook a couple of months ago (post- 2.0 upgrade) during a forced shutdown, but could never find it again. Has anyone else seen it?