I happened to be looking for a little information on threading and how the thread pool works when I stumbled across a project at www.grid.org that I found pretty interesting.  It works in a manner similar to http://www.seti.org, but instead of looking for life, it's trying to save lives.

You download a small program to you're computer and leave the program running all the time.  This program contacts grid.org (and/or their parent organization, United Devices) to download chunks of research data to your PC.  When your computer is on, but not in use, the program analyzes that data to help aide cancer research.  It's all about the key and lock mechanism that certain molecules have with proteins, but I'll leave that for to you to check out.  :)  Your desktop may not discover the cure, but with millions of idle computers around the world, it sure would speed up he process.