If you've used it, you know that the service, and its perks and merit badges, can be addictive. And if you haven't, you should know that hip venues will often give their "mayors" (Foursquare users with the most check-ins on record) little but much appreciated bonuses, like a free beer. Moreover, Foursquare is a new way for media organizations to plug their knowledge into the social grid. Magazines that review restaurants, for example, can provide "what to order" tips accessible to readers who check in at venues that the magazine's critics have covered. There are, of course, problems with the network. For one thing, it's pretty much run on the honor system, making it increasingly vulnerable to fraud as its user base (and the dangled rewards) increase. But if you're looking for the next Twitter, even if only to avoid it like the plague, this may be it.