Unless you're a hardcore computer user cracking out some serious number crunching, or permanently playing the latest and greatest games, then chances are your CPU power is going to waste.
Folding@home is a distributed computing project that analyses how proteins fold or misfold. When a protein misfolds, it can lead to diseases such as Alzheimer's, Mad Cow Disease (BSE), CJS, ALS, Huntington's, Parkinson's disease and many forms of Cancer.
The Folding@home client runs invisible to you, working away until you need your CPU, then the client waits patiently for you to finish fragging the bad guys and saving the world, when it will continue folding.
If you want to help the human race cure disease, without any cost to you, visit the Folding@home web site, download and install the client, and let time do the rest.
I'm a member of the Fedora Folders, a group of Fedora users who contribute to the Folding@home project. If you want to join our team, see this thread on FedoraForum.org for our team number and how to setup the client on Fedora.
My personal statistics are available here and in more detail here, the team statistics are available here and again, in more detail here.