I used to carry mine around so I could build up the play coins, and I'd get a ton riding the metro. There was also a neighbor in my old building who played, but I couldn't figure out who irl. Now I live in an older neighborhood and drive and leave my gameboy at home and it's lonely. I should carry it in my handbag.
Yeah, buses and the subway always get me a couple! I can't help but wonder who it is, though. I almost never see someone actually playing on their 3DS, yet I still get streetpasses!