That’s not to say that nobody’s tried it.
That changes today with Foursquare 1.9 for the iPhone.
Here’s a screen shot.
Personally, I prefer the news feed view – maybe because services like Twitter and Facebook have conditioned me to this format – but it’s hard to argue against a geosocial service introducing a map to help you find your friends.
One other update with this version – improved graphical assets to take advantage of the iPhone 4’s retina display.