whoa... nice angle. I wouldn't buy it myself, but it seems plausible that lots of people would.

One thing: consider slightly different angles on this. For instance, a mosaic of all photos in which a person is tagged. And/or in which their friends are tagged. Furthermore, you could break this down into years, such that a person could have one poster for 2010, buy another one next year for 2011, etc. etc.

Also, think about the corporate angle here: I'm sure corporations would live this kind of thing... visual represenatations of the community who connect with them on FB. Hopefully you could sell premium versions to corporations to hang in their foyers: larger, better quality finish, whatever (you'd know better than I). Good luck :D