stolen from Gizmodo

http://www.climateprediction.net/index.php

If you run your computer for long periods on end without using it (bro, mind, etc) you can use your spare mhz to do some calculus for the greater good...

Total Model Years - 18,679,047.078
Trickling Machines - 60,526
Completed HadSM3 Runs - 169,628
Completed Sulphur Cycle Runs - 13,537

...well, we all already knew it, but still:
http://www.sueddeutsche.de/kultur/artikel/631/90541/