Google Latitude allowed users to share their exact location on a map until now. It was easy to keep track of where people were going but personally, it did not make sense checking into an exact location. Starting Google Maps 5.1 for Android, this has changed. Now, users can check in at real places instead of simple addresses.
The Check-in system works as an add-on to the Latitude automatic update system. Thus, while you are automatically updating your location with Latitude, you can additionally check in a place to tell your friends your whereabouts. Now, how is this different from Foursquare?
Google Latitude check-in allows you to check in automatically, has check-in notifications and checks you out of a place once you have moved out. Latitude has mentioned those three features and none are incorporated by Foursquare yet.
Other than that, it has an equivalent of Mayorships and allows you to get a turn-by-turn direction to the place. The feature is not complete yet and it will be a few days before you can see your history of activities with Latitude. The latitude service was long ignored and now that geolocation based services are catching up and Marissa Mayer is heading this area, we will see a rapid improvement in the sector.
See the feature in action in this YouTube video.