The Geo-Social  Network jungle now has a 500 pound gorilla in its midst.

The launch of “Facebook Places” may well be the death knell for Foursquare and Gowalla who have been the darlings of the space to this point. Or will it?

Facebook product manager Michael Sharon describes Facebook Places as a feature that lets you tell your friends about new places and inform them where you are via your mobile – much like Foursquare.  This short video demo explains…

Sharon added: “Ever gone to a show, only to find out afterward that your friends were there too? With Places, you can discover moments when you and your friends are at… the same place at the same time. You have the option to share your location by “checking in” to that place and letting friends know where you are. You can easily see if any of your friends have also chosen to check in nearby”.

Wirefresh summarises how it works quite succinctly: Once you’ve got Facebook fired up, you can hit the “Check In” button to see a list of places near you, and once you’ve selected the venue you’re at, your check-in will create a story in your friends’ News Feeds and show up in the Recent Activity section on the page for that place.

When checking in, you can also tag friends who are with you – like you might tag a friend in a status update or photo – and you also can post an update along with your check-in to tell folks what you’re up to (e.g. I’m going to the boozer to get smashed”).

The “People Here Now” section lets you see who’s already checked in with you at that place, although this is only visible for a limited amount of time and only to people who are checked in there.

The idea is that you can find people who share your interests and see who’s out and about near you, although there’s the option to uncheck the “Include me in ‘People Here Now’ after I check in” settings in privacy control in case you want anonimity.

Facebook Places is only available in the United States right now, but Facebook say that they’ll be making it available to more countries and on additional mobile platforms soon.

It remains to be seen whether this kills of the other major Geo-social platforms but with the inertia Facebook has with its existing member base (500+ Million worldwide) to promote the service, it certainly looks ominous for them.