The PS3 -- it helps researchers learn more about various diseases with the aid of Folding@Home. It helps us feel good about ourselves (and impress our science-addicted friends), knowing we're making some kind of difference, despite how marginal it may or may not be. What hasn't been talked about on this site yet, specifically, is the cost this really does inflict on you, the selfless consumer/pseudo-researcher. IGN wrote up an article about exactly that.
The cheapest state to run Folding@Home is Idaho, at 4.78 cents per kW hour -- running the program for a month straight nets you a bill of $6.88. The most expensive is Hawaii at 19.28 cents per kW hour ($27.76 for a straight month). Georgia? Near the middle -- 7.31 cents per kW hour ($10.53/month).
We're not trying to dissuade you from running the program! That's for running the thing an entire month straight. We don't know if a PS3 could actually handle that (if I had an extra $500, I'd do a huge piece on it with a webcam 24/7 to show you it's always on, but nah). It's safe to assume that cutting the monthly price in half will be what to expect from running your PS3 -- gaming included.