In my opinion, if there were extraterrestrial life out there, and they were more intelligent than us, I think they'd find us first.
And I really don't care much for them, unless they can end all our miseries with scientific/technological wonders and
not conquer and make us their pets.
But as distritubed computing goes, I think if you are oging to choose one,
Folding@Home is the best one to run.
There's also
GIMPS, the search for Mersenne Primes, but I think folding is more important/helpful.