When I was in Vegas I tried out foursquare and I haven't stopped using it since. I like how it adds another aspect to Twitter and Facebook posts. I also like adding locations and tips. And I really like getting badges and becoming mayor of locations.
Now when Aaron and I are going to Wegmans we are jostling each other to check in on our iPhones before the other. It kind of peeves me that he is the mayor of our house. Hmmphhh.