"Of course, at that time I thought that social networking sites were a complete waste of time -- both for the users and those developing the sites -- so I earnestly tried to talk Mark out of squandering his precious Harvard education on such a frivolous endeavor. "You think you're going to compete against Friendster and Orkut?" was the general outline of my argument. There were already too many social networking sites out there, I claimed, and building yet another one was clearly a waste of time."
Interestingly the argument against building a social network is still the same, and inevitably someone will come along, not listen to the advice and create the next facebook. These things seem to be cyclic in nature.