I would LOVE to have one but haven't made the decision yet. I am going to talk to my doc when I go in on Friday. If their regular time for the u/s is 20+ weeks, I will have one done privately. I found a place around here that does it at 16 weeks (right before Xmas!!!), but I don't see paying the $99 for it, if they are going to do my regular one at the same gestation, or even at 18 weeks.
You would think as close as I am to DC, that there would be tons of options for this, but sadly they are few and far between 