Scoble missed a bunch of steps. According to my recollection (FaceBook member since Sept 2004), it was:
Phase 1: Harvard only.
Phase 2: Ivy-league only.
Phase 3: Top schools only
Phase 4: Top schools and their alums only.
Phase 5: All colleges
Phase 6: All colleges + high schools
Phase 7: Everyone
Phase 8: Everyone + app makers
Phase 9 (not sure on the timing of this, I forget if "I Support X" pages came out before or after the platform): Everyone + app makers + political causes
According to Robert Scoble, the controlled pacing is still going on:
"Here’s the phases of Facebook:
Phase 1. Harvard only.
Phase 2. Harvard+Colleges only.
Phase 3. Harvard+Colleges+Geeks only.
Phase 4. All those above+All People (in the social graph).
Phase 5. All those above+People and businesses in the social graph.
Phase 6. All those above+People, businesses, and well-known objects in the social graph.
Phase 7. All people, businesses, objects in the social graph."
http://scobleizer.com/2009/03/21/why-facebook-has-never-list...
[1] http://www.unc.edu/depts/jomc/academics/dri/idog.html