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.