Well for me anyway, keeping track of the people I meet throughout my career is kinda... impossible through conventional means. This due in fact to how many of them there are and that they get scattered to the four winds to various duty stations across the world. So the only way to keep track of the friends I've made is through Facebook. Sure, eventually friendships wilt a little from time and distance, but I'd be curious to see what happens when I try looking them up in a few years.