One such app, called Ditto, combines a user's wants (ex: "I want to eat oysters.") with recommendations from friends (ex: "Go to Hog Island Oyster Company in the Ferry Building in San Francisco."). Users can also elect to accept recommendations from other people who may not be a part of your friend circle.
It's a natural extension of apps like Foursquare and Gowalla, in that it allows you to join forces with friends if you don't feel like visiting a certain place on your own. But to me, this just seems like one more app to check if you're looking for something to do. Not to mention I usually have reasonable success recruiting friends to join me via Twitter postings.
Would you use an app like this?