My grandfather has had alzheimers for 15 years now, and he's at the point where he can no longer do anything (walk, talk, feed himself, etc), so i have a "reason" to be doing this too. The competition aspect is good though, and it drives people to help out more
And hopefully one day noone will have to deal with these horrible diseases
Out of all the distributed computing projects, this one just seems like it has the best chance of actually helping humankind. Looking for intelligent aliens isn't going to help us (SETI), they'd probably be extinct by the time we got the radio waves anyway.