Must be all the riff raff
Seriously though, I'm not sure what some of you are expecting (in terms of waves, thumbs up, etc.). I really never look at or attempt to interact with other drivers (unless it is to provide them with my own, uh, negative feedback). To me, it seems too likely any gestures could be misinterpreted, plus I'd rather spend time looking at the road, other traffic, etc., than paying attention to other drivers, regardless of what car they are driving.