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
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
Phase 10: Everyone + political causes - app makers except Zynga.
Phase 11: Everyone + political causes + businesses + Zynga
Phase 12?: Everyone + everything?