There's also a widget (systeminfowidget) that shows the load on a widget. Handy if you don't want to leave the terminal running but seems to consume a few % load by itself (at least while the desktop is visible). I'm not sure what repo it's in though (I've got all of extras, testing and devel). The app manager doesn't seem to tell you where an app comes from and my apt-foo isn't high enough to figure it out from the commandline.