It seems that Yelp has decided that reality isn’t good enough, so they augmented it. After opening the app, make sure you are on the “Nearby” screen & shake the device three times slowly. (like counting to three).

A button in the upper-right-hand corner will appear named “monocle” tap on it and move your the iPhone around to view the labels spinning around you. Realize this only works on the iPhone 3GS.

Have fun!