AlexC at pstupidonymous has a good post on Bumper Stickers.
I have one of the rare W04 Bumper Stickers in Boulder. When I encounter another, I sneak a furtive W sign at the other interloper, hoping that the natives will think I am flipping him off.
But when I parked at the airport -- every car that had a sticker had a Bush sticker.
Not a statistical sample but I thought "that's our demographic. We work, we go to the airport..."
Am I mad? I always see the GOP folken as the middle tier: rich folks and poor folks are Democrats, high-school dropouts and PhDs are Democrats, the GOP takes most of its half out of the middle, and those are the folks at the airport. Broad brush, of course, but I think it holds.