I believe SETI@home is the best possible use of my CPU idle time. I ran distributed.net for almost 2 years, and did nothing but waste time cracking encryption. Searching for extraterrestrial life seems a bit more practical.
SETI@home and Astropulse are funded by grants from the National Science Foundation, NASA, and donations from SETI@home volunteers. AstroPulse is funded in part by the NSF through grant AST-0307956.