This thread reminded me of something I should probably share with you all, if you haven't already heard of it:
What it is, is software anybody can install in order to contribute to Stanford University's research into protein folding and misfolding. The way that proteins fold is a very complicated process that takes a lot of computer resources to simulate.
Fully understanding protein folding would be a major breakthrough in understanding the causes of a wide variety of diseases, including: sickle-cell disease (drepanocytosis), Alzheimer's disease, Parkinson's disease, mad cow disease, cancer, Huntington's disease, cystic fibrosis, osteogenesis imperfecta, alpha 1-antitrypsin deficiency.
Instead of using expensive supercomputers, Stanford's chemistry department uses distributed computing to create a supercomputer over the internet, made up of thousands of PCs, like yours. In doing so, they've created the world's most powerful supercomputer, which over the years, has broken records, even competing with IBM in terms of its processing power.
The software runs in the background or can turn off and on, when you're idle, so doesn't really affect system performance.
So far, the project has led to some scientific success, with a few dozen academic papers published and more still to come.
You can read more here:
If you own a Playstation 3 gaming system, you can install it on that... I'm not too sure about the min. requirements for PCs, though.