It seems to me that if Facebook is going to retain and data-mine your info when you quit, it might be worthwhile muddying it up before you leave. So instead of retaining all your friends and applications, what if you had a program disconnect them all, then make some random searches and request them as friends? Next, delete all your applications and start fresh with more random searches so that the data Facebook gets for "you" in their unpersons archive actually represents a collection of random noise of no value to anyone.
Mokalus of Borg
PS - Apparently they are holding an all-hands privacy meeting this week.
PPS - They probably want to increase the feeling of privacy without increasing actual privacy.