I'm a big fan of distributed computing projects. I think it's my Wyoming/Midwestern background of "Use it up, make it do, wear it out or do without" that makes me like the concept of using every last cycle of my CPUs. That, and the desire to help in finding a cure for Cancer/Alzheimers/Mad Cow, etc.
I use Folding@home on pretty much any machine I get my grubby little hands on. So far the team I created and which consists mostly of my machines has done enough folding to reach the "top 1000" contributors to folding. At that point, the folding@home website gives you a special "fast page" though I'm not really sure what value that provides. It's worthwhile to note that I created the team back when Nikki and I still didn't know what last name we were going to use, so it is "Addison" when it should probably be Knaddison. I'm working on getting it fixed...it's not easy.
Of course, I urge you to install folding@home on your machine. Unless you have extremely limited amounts of RAM (like 128MB), it is not noticeable on your machine. I believe that it does not hurt the machine in any way based upon this forum thread. So, without any further justification, just download it and start running