Heard of Folding@Home? Its a bit like seti, except it uses pc power to help make new medicines etc. This is a nice article from /. saying basicly that arguments against running it (pc performance hit yadda yadda) are rubbish.
"THERE ARE A FEW legitimate reasons not to run Stanford's Folding@Home client. You could be without an always-on Internet connection, or barely able to scrape together enough change to make your next utility bill payment. Heck, you may even think that searching for aliens is a better way to spend your spare CPU cycles, and that's your choice. However, some have raised questions about whether or not the Folding@Home client has an impact on overall system performance, something that could prevent individuals and especially businesses from running the client on their machines. "
Download: The client