Everyone knows Facebook is the massive presence on the internet and is fighting to get more user interaction on many fronts. Deals with bing and skype are still going strong but there are some battles they have backed off on.
To be fair they still have check-ins but it's now just part of a post. Not a key feature of announcing where you are. But still FourSquare use of gamification, deals and very good location database made this a battle facebook was certainly losing.
Everyone has had a go at the "group by" systems pioneered by groupon. Google and Facebook both trialled getting into it but Facebook has now given up. Will be curious to see if they pick one to partner with or just enjoy all the traffic they bring back into facebook and advertising revenue they hand over.