At my house, I have an Ubuntu server setup to store/share files, stream music, develop web sites, and some other things.  I leave it on all day because it serves as the print server for all the family computers, so I figured I could put it to some use.

Incase you've never heard of it, Stanford's Folding@Home project is a massive distributed computing grid, using the processing power of thousands of personal computers' idle cycles to simulate folding proteins.  I'm no scientist but on their web site they explain that folding is how cells work in the body.  When these cells mis-fold, it causes diseases like alzheimer's and mad cow disease.

So I installed the Folding@Home client on my server.  I wonder why more people don't set this up.  It adjusts so that the process doesn't suck all the CPU resources.  The client reports to the servers at Stanford to record both my stats and overall team stats (I joined Team Ubuntu.)

If your computer is on for more than 6 hours a day, you should take a look at it.  Folding@Home has a client for just about every computer operating system, so users from Linux, Windows, and Mac can all help out.  There's also support for multi-core processors, so you can run a client for each core.