I used BOINC at one time, but I only did a little more than nothing with SETI@Home. On a slightly related note, I used Folding@Home far more, and I'm on the Ubuntu F@H team.

In other news, I very highly doubt you could catch anything from a distributed computing program, unless the upstream computers are infected, but that is also extremely unlikely, as (I think) they all run Linux or some form of Unix.