The interwebs are alight with discussions about Facebook‘s new location-based checkin service Places. Among the flurry of info and debate about its value, one thing may have been overlooked: The secret ingredient of the system that may end up making Facebook a lot of money. Because as well as trying to attract users, Facebook’s also trying to attract local businesses to build Facebook Place pages, and associate their Facebook presence with a location.

For now it’s a slightly complicated affair to get location data into your Page if you’re a business–involving creating a new Places page, and then associating the two together. It even looks like not every business page owner can do this final piece of the puzzle yet, and Facebook seems to be alerting specific people about the system. Quite apart from this foible, the Places feature is pretty powerful, and notionally works much like business-owned pages in Yelp. Essentially you build a PR page, and then try to attract fans who’ll then checkin when they arrive at the site. Fans get to “play” the location game, businesses get to work out who their clients are–for promotional purposes or even (if they can get hold of demographic data) for business planning or targeted marketing reasons.

But Facebook is the engine behind all this, don’t forget–the worlds largest social network, with data on over 500 million users. Stripping the concept of Facebook to its core, one realizes that Facebook’s biggest bankable “value” is the structure of this network (with IDs for each user) and the web of links between friends–everything else about Facebook rests on this core.

If you have a locally based business the new Facebook Places is something to watch.