I guess the larger point is: he didn't spend much time telling people how great facebook was. He created something with utility and rolled it out in a way that would provide maximum utility to each additional person signing up. (Replicating existing networks in order of diminishing prestige)
He wasn't even the first person to come up with the idea at Harvard. Heck, there were two similar projects at Cambridge when I was graduating in 2000. And a dating site.