1. I joined because I was bored. I figure this provides some sort of karmic balance to my evil BitTorrent usage. Hope my CPU cycles help!
2. As long as the science doesn't involve spraying liquid in something's eyes, I'm all for it.
3. Take out some advertising in newspapers or something. Plenty of people have fast enough machines to help.
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.