Boopie and I have actively participated in this since Sept of 2004. We got started after reading a book by Steven Hawking. It's fun, the computer does all the work, and the explanation below tells how it works and how it does it. It's very interesting, if you're interested in the unknown. People all over the world participate in this. We're are members of the Georgia Tech Team with over 500 members in that group alone.
Here is a copy from one of the scientists at Seti that explains what SETI is:
What is SETI@Home?
SETI, or the Search for Extraterrestrial Intelligence, is a scientific effort seeking to determine if there is intelligent life outside Earth. SETI researchers use many methods. One popular method, RadioSETI, listens for artificial radio signals coming from other stars. Seti@home is basically a RadioSETI project that lets anyone with a computer and an Internet connection participate.
Seti@home is a scientific experiment that harnesses the power of millions of Internet connected computers in the Search for Extraterrestrial Intelligence (SETI). You can participate by running the free BOINC client program that downloads and analyzes radio telescope data. There is the small but very captivating possibility that your computer will detect the faint murmur of a civilization beyond Earth!
Seti@home uses the largest telescope in the world, the Arecibo telescope in Puerto Rico, to continuously scan the sky for radio signals. So far, nearly all of the sky visible from the Arecibo Telescope has been scanned at least once. As time progresses, the Arecibo Telescope passes over the same point several times. This benefits Seti@home, because it allows us to distinguish between signals that occur due to radio frequency interference and actual extraterrestrial signals. After the data is recorded onto tapes at the Arecibo Observatory, they are shipped back to the Seti@home lab in Berkeley, California. The data is then broken up into work units (WUs), which are sent out to the BOINC client program over the internet for analysis.