Tyler Cowen's and Robin Hanson's opinion: It’s about signaling (a term of art in economics). Your preferences in fiction, and the way you articulate those preferences, signal your attitudes, values, and ideas to others. Fiction thus serves as a way of
“getting people in touch with each other.”
Basically, they are saying, you read the kind of stuff you do because of it serves as a social marker: it benefits you personally by helping you connect with similar people.
Cowen points out that the kind of fiction you read signals to the people what you are capable of learning about the world and that you look to form alliances and associations with people who also appear to learn the same things.
Does that explain why people (ok if not all, at least the avid readers) check the bookshelves of people they visit? I accept that Cowen's and Hanson's contention probably does explain a part of the picture. One thing that reading and choice of reading material allows you to do is to present to the others that "I am this sort of a person with these kind of tastes."
But I am not entirely convinced by the argument. The same can be postulated about virtually anything — music, movies, food.
Reading fiction is not valuable only for what it "signals" about you (as too is the case with music, movies, and food). I am sure pleasure plays a significant role in it — to be a part of worlds (and themes, values, etc) that you find interesting and appealing. And the opportunity to create and recreate these worlds with your own imagination.
Makkad-Man has been slinging from inbox to inbox in my office for the last few days. Very hilarious. Do have a look at this adventure of this desi web slinger.
Two hundred years after its publication, Wordsworth's Daffodils has been "updated" a bit and given a 21st century upgrade with a pop video and rap version. 
