RWW: Facebook says its Timeline "tells the story of who you are." That's lofty wording. It assumes that you share "who you are" on Facebook. It also assumes you share enough of yourself to make Facebook Timeline "the" definitive "story" about you. Similarly, Path version 2 calls itself a "journal."
While both these apps are ostensibly for sharing, they're also asking people to use them to store their own memories. Facebook and Path both put great effort into pretty presentations of these memories. But each could change tomorrow for business reasons. If we want to be able to reminisce about this early era of mobile tech, we can't depend on the free, hosted apps we use to share our lives now.