I'm distinguishing between qualified free traffic (search/viral) and spaghetti at the wall free traffic like StumbleUpon or one of those skeevy pageview buying

I'm distinguishing between qualified free traffic (search/viral) and spaghetti at the wall free traffic like StumbleUpon or one of those skeevy pageview buying services. I didn't actually read the post before commenting (!), and I see that it describes some good traffic sources.