Latitude is Google's version of Foursquare and now Facebook Places. It is a location and GPS based check in service integrated with Google Maps. I have been using Latitude before the recent update and needless to say it was lacking in features compared to its competitors. Although it integrated nicely with Maps and even gave directions to your friends locations you never had the ability to check in at an actual place only coordinates on the map.
The new version bundled in a Google Maps update brings the places check-in feature to the app along with some new convinces. You have the ability to be sent a notification to check in case your forget and for places you have checked in before you can set it to automatically check you in and out of the locations in the future. These new additions plus the places built-in yelp results make a viable option in the social check in arena. Now the only task is getting the word out so more people actually take advantage of this utility and make it worth while.