The Wall Street Journal is reporting that Facebook is negotiating with Microsoft to sell a stake in the hot social network at a valuation between $10 billion and $15 billion. That would net Mark Zuckerberg's company between $300 million and $500 million in cash, without Zuckerberg having to surrender any meaningful control over the company; the stake would represent 5 percent or less of Facebook. What's not clear is why a deal's happening now, save to lock in a stratospheric valuation. Some time ago, a Facebook insider called Zuckerberg "a crazy kid" for not selling. And we've said Facebook's valuation claims seemed a bit puffed-up. But given that suitors' offering prices have rocketed tenfold since then, Zuckerberg doesn't seem that crazy anymore. Instead, it's Microsoft executives, driven mad by Google and MySpace envy and determined not to miss out on the social-networking trend, who seem, well, a bit off.