I was reading Mac Format this afternoon at Barnes.
The author states not to throw old Macs away.
Here are ten things you can do to an old mac. Kind of like an old PC thing...
1. Use it for photography.
2. Backup all of your important data files.
3. Turn it into a file server or (music server).
4. Give it to the kids.
5. Use it for music, photos and movies.
6. Further the cause of science
www.stanford.edu/group/pandegroup/folding.
7. Use it as a home automation device
8. Mod your mac and give it a new look
9. User your old mac for home security
10. Learn a new operating system and install a Linux
More info about them here at Mac Format issue 188.

Enjoy,
Levi