I remember back in the 90's that every time Bill Gates sold 1 or 2 percent of Microsoft, people would freak out that Microsoft's collapse was imminent. Even though he did it every six months.

Whatever you think of Facebook, it is extremely prudent for Zuckerberg to diversify. If he had $1 million in non-FB assets, he would still have 99.99% of his assets in Facebook. That's a crazy amount of his wealth concentrated in one stock.