At first you just posted to Twitter or Facebook that you "just got to Target" or "finally hitting Starbucks for some much needed coffee". Then Twitter added features to allow you to post your location along with your tweet but you still had to tweet where you were. The location feature just posted a link to the map coordinates of where you were. This created a gap in the Social Media landscape that Location Based Check-In services evolved to fill. Gowalla, Foursquare, Loopt, Yelp, and now Facebook Places are examples of this Social Media evolution. Each has its own unique take on the Check-In process but all are generally the same at a base level. Opening each app begins the location portion of the service and you are then presented with a list of Businesses, Venues, Restaurants, etc... that you can Check-In to if you are close enough. Each app has a form reward system for being the person to check in the most at a particular location.
- Gowalla has a general Leader Board for each location but focuses more on random virtual goods that you "find" by checking in. You can collect these or drop them at locations to become a "Founder" (for the first few to check in) or swap items to find rare ones that you don't have in your collection. Gowalla tracks your achievements thought Stamps in your Passport for things like posting pictures, achieving a certain number of check ins, and unique stamps for each State you check in to.
- Foursquare awards "Mayorship" of a location if you're the one to check in the most number of times in a particular period. You also earn Badges for certain goals similar to Gowalla's Stamps.
- Yelp is more of a Review site but recently added Check-In ability and awards titles of Duke or Duchess for those that check in the most at a location.
I don't use Loopt or Facebook Places frequently enough to know what their reward system is like but so far I've not heard of one for either.
Since Yelp is already established as a general review site/app, Gowalla and Foursquare are the leaders currently duking it out for supremacy in the Location Based Social Media game. Foursquare is rapidly being embraced by the Business Community with deals, discounts, and specials offered to the Mayor of a location or simply for checking in. Gowalla recently entered into a deal with Disney and will award you unique Stamps/Buttons for check ins to each of the Disney Attractions. Gowalla also has a feature to allow users to post travels that people can recreate by following your check ins. (sort of a "follow me" tour of an area). This feature was also part of the Disney deal.
I see neither service rushing out to be an overall leader. Instead I see each becoming a leader in their own arena. Foursquare is looking to be the leader in the Business end of things while Gowalla is looking to become the leader in the Recreation arena. The Disney deal gives Gowalla a strong lead on that front and other parks and venues will probably follow suit. Add to that the fact that the new Gowalla v3.0 iPhone app now uses the Facebook and Foursquare API to allow you to use one App and check in to all 3 services as well as post updates to Twitter. That fact might help push Gowalla into the lead a little bit since nobody wants to use 3-5 different apps just to get all your check ins done. I like the new Gowalla v3 app and use it as my main one for check-ins. One App to rule them all as some would say :)