His post got me thinking about combining Four Square w/ Yelp. (Feel free to laugh.)
If Yelp cannot buy Four Square, at least there should be some kind of partnership. I think this will help them both.
Turn all the annoying things in a city/turn into a friendly, fun activity: directions, restaurant reviews, hard to find places with no signs, etc.
Let's say you just moved to a city and find it someone dumped their dead pet (eg boa constrictor) on the street. You type in, "Who do I call to get rid of it?", someone posts the answer, and you both get a reward for improving the city (and the world).
The idea is to turn life's annoying problems into a fun puzzle to solve with a group of people spread around the world.
I doubt Yelp, Foursquare, or I would have the imagination to refine it. But you do. "Every problem becomes an opportunity for fun."
But, it gets better! You also get to compete against Craigslist and AirBnB. Maybe it would be fun to compete against 4 major competitors who have TONS more resources than you. People would be expecting you to fail majorly. Now that sounds like fun.