Found via Lifehacker I found IOGraphica a little programm that tracks your mouse activity. It draws lines when you move your mouse around and and filled out circles if the mouse remains somewhere. on the screen.
Below you see my mouse activity during. The recorded movement shows 4 hrs on a mac while i was busy updating WordPress and fixing some bugs in another blog I administer.
The program is available for Mac and Windows and can be downloaded here for free.