Facebook has jumped on the location check-in bandwagon with a new feature known as Places. Facebook Places has launched with four partners, all services that already offer check-in services — Foursquare, Gowalla, Yelp and Booyah.

If you use Foursquare, Brightkite or other location check-in services there isn’t much to see in Facebook Places. The only real difference is the scale that Facebook brings to the table.

Places is already available to most in the U.S. in their desktop browsers on Thursday. To use Places on your mobile, you’ll either need to download the new Facebook iPhone app (version 3.2, which is available now), or you can head to the Facebook mobile site with a web browser that supports the Geolocation API (basically anything but IE).

To read full coverage of the Places launch announcement on Wednesday night, read Ryan Singel’s report on Wired’s Epicenter blog.

While Facebook isn’t doing much with location that hasn’t already been done at least half a dozen other services, it does of course bring location sharing to Facebook’s massive user base of 500 million people around the world. Eventually, all of them will get access to Places once it rolls out in other countries. In the past that user base hasn’t been very welcoming of new features, especially features that involve privacy changes. While Places will be activated for all accounts, by default your location won’t be broadcast to everyone — just your friends.

To use the new feature, you can actively check in to a location, or you can let your friends check you in to a location without doing anything. While this may ruffle your feathers, if you don’t want people knowing where you are, it’s pretty simple to disable your friends’ ability to check you in, and to just ignore the check-in button.

According to Facebook CEO Mark Zuckerberg, Places has three goals: helping people share where they are, seeing which of your friends are close by, and seeing what other places of interest are near you.

For the first two there’s a feature called “People Here Now” which shows you who else is also at your current location. The what part of the equation is murkier, though each place has a map with pins denoting nearby friends and locations (business data is pulled from Localeze). Facebook’s Places also offers a feature that allows businesses to “claim” a place, which then turns it into a Facebook page.

As for Facebook’s current Places partners, two are broadcasting their data to Facebook and two pulling Places data into their own sites. Foursquare and Gowalla are both broadcasters — your check-ins on either site are passed on to Facebook (for now the API is one way, so if you check in through Facebook, your Foursquare account will not be updated) and your location is updated on both services.

In the case of Yelp, your check-ins are pulled out of Facebook Places and added to Yelp reviews. Booyah also pulls in Facebook location data as part of a new iPhone-based game, InCrowd (set to launch soon).

For developers there are some new API hooks to take advantage of the new Places feature, though for now the Places API is read-only. A Write and Search API is currently in a closed beta testing phase. Head over to the new Places API documentation to learn more.

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