I've frequently seen this strange little plastic gizmo (circled in the image) and wondered what its purpose is. I'm tired of wondering -- do any of you know? What is it even called? (Don't ask how long it took to find that image...)
Not all cars have them, but I've seen them on 80's cars and new ones, cheap micro cars and "respectable" sedans, but never on really nice cars. It's certainly not a window guide, and I doubt it's aerodynamic. In this picture it seems to extend backwards behind the rubber trim, but I've mostly seen them extend outwards a bit. The whole thing is no bigger than a sugar cube, and is affixed to the frame of the door (doesn't attach to the window, or even touch it).