1. I run SETI @ Home because I think it is a project well suited for the distributed computing model.
2. While exploring the possibility of contacting extra-terrestrial intelligence may not be a high priority for the government, it is something that we as humans want to do and should do. It is my opinion that it's worthwhile to donate computing time for that cause.
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.