I believe that there is extraterrestrial life, but I'm not sure if we'll ever find it (or they find us). Think about it - the volume of space in the universe is gigantic! We've only been sending signals out into the universe for a century or so; how many stars are within 100 light years of us? The odds of running into another intelligent species are, literally, astronomical.
So why do I run SETI@Home? Because sometimes the odds don't tell the whole story.