you make a compelling point. there IS a treasure trove of data that can indeed be mined from the BDS application.
From a pure startup company standpoint, i don't think BDS is entirely a bad idea. it's taking a part of facebook that is otherwise boring and lifeless, and spinning it off into it's own thing.
this is a good business model, i think - - taking existing pieces of large websites like facebook and turning them into their own business.
twitter = status updates.
instagram = photo sharing.
foursquare = "checking in" to places
birthday slam could very well be a way to invigorate a part of facebook that is wholly useless besides its sole purpose (which is to remind to of friends' birthdays), and spin it off into something that is much more - - something imaginative, something with incentive, prizes, points you can earn, and so forth.