I've been having a blast with foursquare for the last two months. A lot of people hate the location-based check-in service, but I don't think they get it. Sure, it's another way for vain people to use the Internet to share more mundane details of their mundane lives, but foursquare can be fun and useful. I love checking out where my friends eat, drink, and shop; I'm more likely to try a restaurant an IRL friend likes than a random one. The baseball lover in me marks out at all the stats available on foursquare; it's interesting to see the patterns and statistics of your social life.