If you’ve not seen this yet, you have to check it out. Awesome time waster from any machine that has Internet access.
It’s not a game per se, but a toy. Draw a line, hit play, and a little dude sleds down whatever lines you’ve drawn. Bump him too hard, and he gets knocked off.
You can save your tracks, but note that it saves them local to your PC in a Flash directory. The save file is limited to 100k, so eventually you get to the point where you can’t save any more (and it’ll just silently fail to save the track). You can nuke this file to start over. It’s in:
C:\Documents and Settings<Username>\Application Data\Macromedia\Flash Player#SharedObjects<Some Hash>\ic3.deviantart.com\fs12\f\2006\292\a\1\Linerider.swf
YouTube has tons of videos of pretty damn amazing tracks people have made. Here is a submission of mine, a system which slowly increases in energy and eventually crashes.