I do this all the time. And it's not limited to when I'm on my biek either. If I'm walking, I'm pay close attention to the messengers and their rides. If I'm driving, I check out the bike on the roof rack first, then the person driving the car. I also look at people's bikes as I pass them or they pass me when I'm driving. My wife gives me crap too. I should be watching the road and not the bikes on the car in front of us. She makes fun of me most times too! "Oooohhhhh, look at that bike. Look at it's wheels!! Aww shucks... too bad, it's got gears!!"