Someone please take Facebook's knife and fork away.

For some iPhone users accessing Events pages on FB, a new “Check-In” button now appears.  Facebook, it seems, has taken yet another page from Foursqaure after its introduction last summer of Places.

The “Check-In” button only appears on the day of the event. Users must also be geographically close to its location. And while little is known about other applications of the feature, it’s safe to assume that it will complement both FB’s Deals and Events, presumably allowing folks to someday check-in to locations and win promotions, a la Foursquare and Groupon.

Strangely enough, Foursquare, along with competitor Gowalla, helped Facebook to develop Places. So maybe this, too—their death knell—was also their doing.—Devin Chanda