I really don't do much when browsing, though. Dictionaries, encyclopedias, Mapquest, Scottrade, vBulletin, a grad school board, .edu sites, email, imageshack/clicking on pictures here... I don't really go to sketchy places. Then again, I don't know how easily looking at, e.g., a friend's Myspace/Facebook profile, tinypic or similarsuch affects my computer's security.
My only virus problem in the last year has been the VISTA VIRUS. And for some annoying reason, I can't seem to get rid of this damned thing.