Businesses register with Foursquare, but people also enter their own homes, streets, and hangouts, so that when you check in to a particular place you can see what other people have to say about it, and even who else is there.
While sites like Foursquare, Gowalla and Brightkite can be fun to share location with friends, they can let not-so-good people know where you are not, potentially opening you up to be robbed or worse.
The biggest shortcoming of Foursquare is that each user has to "check in" to each venue to update his or her location, unlike the passive updating done by Verizon Family Locator and Google Latitude.
TweetDeck: One of the most powerful ways to access all the different social networks is this social browser, giving you access to Twitter, Facebook, Foursquare, and Google Buzz all in one place.
Some businesses like Starbucks have created "Barista" badges in cooperation with FourSquare, which customers can earn by showing up at the coffee shop.