There are apps like that. I've worked on a facebook/iPhone app exactly like that. Problem is that they don't get popular. It's the social game apps and simila

There are apps like that. I've worked on a facebook/iPhone app exactly like that. Problem is that they don't get popular. It's the social game apps and similar trivial things that do well on facebook & social networks. You got to realize what people use facebook for. And there is a bit of a chicken and egg review db problem there. You got to get 20 of your friends to start using the "Food" app hardcore.