I've been running Folding@Home for years. As much as I think the Astronomy stuff is fun, this project has direct medical implications, and I think is more worthy. There are already several published papers which have moved research in to several diseases forward in significant ways.
http://folding.stanford.edu/
Plus, they have a GPU client which absolutely
slaughters CPU throughput.
I run a dual GPU card (GTX295 which I only got a few weeks back) and push through about 12,000-14,000 points per day, that's without trying to use the Quad CPU in my machine. I've nearly put through more points since I got this card than I did over several years with the varying CPUs I've had.
If you have a PS3 that's connected to the net, it has a client built in. It also absolutely flies through work units as well due to the CORE processor.
But Starkler is right - power increase is a factor (especially when using the GPU). Not so much when using the CPU though, if you leave yous machine on anyway (I need to for work purposes)