I just turned down the one at Minifobette's 6-month checkup (at our doctor they do make a point to mention that it's optional--but recommended--when they're going through all the other vaccines.) I told the pediatrician, "Nah, I'm not worried about it, we don't really get sick."
Of course, just two days later we all got a cold.
Minifob got it first though, and I'm certain he picked it up in the waiting room, playing around the other sick kiddos.