I've seen such drinks on cooking/food shows, but have never run across them "in real life". However, being a 39yo married father, I don't tend to frequent bars and fancy restaurants often. I was always under the impression that the N2 had dissipated by the time the drink was served, or that it was used to super cool other components of the drink to allow for physical characteristics not otherwise possible. I wonder if the drink was mixed incorrectly or served too soon.
Chris