It's that time again, that time when I remind you (or tell you for the first time) about Folding@Home. What dat is?, you say.
Folding@Home is a distributed computing project managed by Stanford University, the client program runs on your computer (most major OS's supported) and uses your "spare" computing time to help calculate complex mathmateical formulas. When you're not using your computer at 100%, this client will throttle itslf to use the leftover computing power.

Protein sythesis is a predicable system in which proteins are made by folding upon itself, thereby changing it's shape, and thus it's funciton. Each protein serves some purpose and the shape of the protein determines that purpose. By using a complex mathematical formula, biologists can find out how proteins are made. The problem is that this math formula takes a great deal of computing power. By combining our computing efforts, the aggregate power produced is able to accomplish this feat very quickly and is much cheaper for Standford, and thus the medical community.
Why do I care? It's a great way to show off computing power, or show off team-assembled computing power. I am a member of the SAGoons team, in which my personal computations are also counted in the team overall score to demonstrate how many computations SomethingAwful members have contributed, and to see how your team stacks up against other teams.

More info can be found at folding.stanford.edu. Enter a unique username, and join the SAGoons (Team 150). It's fun to watch your own progress.