I have run Set@Home on and off since August 2001. After a fairly long hiatus, I have added it back to a number of my computers as, essentially, an idle task. Capped at around 25% CPU usage and only running when these systems are connected to power, Seti@Home effectively replaces the idle process on these systems while still leaving them responsive and able to drop into lower power states. And, with that, my user stats should begin to notch up again.

Interesting Links:
My Stats
Seti@Home - as it was in 1999
First Slashdot Story
An early BBC News Story