Daniel Lippman sends me notice of the following:
The Exchange Bar & Grill, set amid the bustling shops and pubs of the Grammercy Park neighborhood, is replete with a ticker tape flashing menu prices in red lettering as demand forces them to fluctuate.
Customers can move prices for all beverages and bar snacks such as hot wings ($7 for 6 pieces) or fried calamari ($9). The prices will fluctuate in $.25 cent increments, but will most likely plateau at a $2 change in either direction.
A glass of Guinness starts at $6 but could be pushed to a high of $8 or a low of $4, depending on popularity.
So if one drink is in heavy demand, its price will rise, causing the cost of other equivalent drinks to drop. A rush on a particular beer would increase its price, and cause other beers to drop.
It is, of course, a marketing gimmick. Daniel also sends along a link on the new idea of eco-sex.