Yelp updated its iPhone app this week and included one very cool easter egg. If you haven’t already, download the update, open your Yelp app, and shake your phone three times. You should get a message telling you that “Monocle” has been activated and can be accessed in the top-right corner of your screen.

So what is Monocle? It’s augmented reality for Yelp. Hitting the monocle button takes you to what looks like the camera application with a Yelp overlay. A compass in the top right corner displays local establishments with a Yelp presence. Rotate your phone to the right spot and you’ll see a little Yelp shortcut card with the name of the establishment. The card scales based on how far away you are, so the biggest cards are closest and the smallest the furthest away. It’s a neat feature, particularly if you’ve just moved somewhere new.

There is one problem, though – augmented reality apps weren’t meant to be released until iPhone OS 3.1. That’s what Apple asked of its developers, anyway. Personally, I appreciate Yelp’s noncompliance, but there are others who think it’s going to hurt the development community. What say you? Sound off in the comments.