Even reading Greenspan's book account, it's clear that he dawdled while Zuckerberg executed. Greenspan frittered around with committees ("'Maybe we should put more emphasis on the Universal Face Book,' I thought aloud during a board meeting" ), kvetched about media unfairness ("'Can we get _The Crimson_ to give us any decent coverage at all?' I kept asking my board, week after week" ), worried idly delaying essential features ("I had considered creating detailed user profile pages at houseSYSTEM's inception, but it seemed like the worst idea possible when students began to fret openly about privacy"), and engaged in redundant academic make-work ("'I can write [a version tracking system],' I offered, not wanting to be the only one without code to write" ).
If tempted to label someone a 'fraud' (as Greenspan did Zuckerberg in a previous HN thread), consider instead that they may be expressing competencies in a dimension you can't readily perceive. Maybe even the very things you're criticizing ("Even though he was clearly smart, he seemed like he had the capacity to go off in a zany direction at any point in time, totally unconcerned about the consequences of his actions. I couldn't figure out any other scenario that would have allowed for the creation of the facemash site." ) are, in fact, strengths.
 Though, Greenspan would still have to contribue a lot to the computer industry to hold a candle to Kildall -- http://en.wikipedia.org/wiki/Gary_Kildall