I use foursquare a lot, I'm a nerd and a fan of stats. I'm also a big fan of the notes people leave behind. Little hints for the new adventurer, or warnings to the unwary: 'Beware the burgers lest you suffer the consequences.'
I started to imagine these notes weren't just tips on the dining. I started to imagine people leaving little chunks of a story. Then you would have to explore the city to find the rest and piece them together yourself. A treasure hunt with words. Hell, since you're going for a walk, why not add in some music for atmosphere? I wanted to live in a world where useless fun things like this exist, so I started doing it myself.
Ideally this is something that people would just discover. A wee surprise for some techie person, and a decent writing exercise for me. The more I've added my own stories though, the more I wish there were others doing it. I live in Glasgow so it's local for now, but I'd love stories from all over the world to be added. Little personal guided tours. A foursquare tale would be a great way to be introduced to a new city.