Because its and ideal way to utilise my spare cycles for a good cause. Although I appreciate the difficulties faced by our current methods its better to look than to do nothing.
Thoughts about ETI
I think that given the size of the universe there "must" be Intelligent life out there somewhere, however given the distances involved we won't meet them in our lifetime unless they come to us.
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.