You spend an afternoon "scrapbooking" in real life, and you get something that your grand-grandsons might, one day, inherit and read in awe.
You spend an afternoon scrapbooking on FB, and in ten years FB goes bust or whatever (Geocities, anyone?), and you've got nothing.
I guess the real test will be my wife -- she loves scrapbooking.
(this, and the first time I went through the presentation my brain was screaming MYSPACE really, really loud.)