* As speculated, Facebook filed an initial public offering yesterday. The social network, which now reports 845 million monthly active users and net income of $1 billion on revenues of $3.7 billion, plans to raise $5 billion. Here’s the letter from Mark Zuckerberg included with the S-1 Registration statement. (Fortune and Wired)

* If Facebook aims for a high-end valuation of $100 million with its IPO, Zuckerberg’s stock in the company would be worth $28 billion. Meanwhile, graffiti artist David Choe, who decorated the company’s office walls and opted for stock over cash, will likely find himself $200 million richer. (The Wall Street Journal and The New York Times)

* Meanwhile, colleague Miguel Helft profiles the man behind Facebook’s IPO, CFO David Ebersman. (Fortune)

* Though AOL’s earnings declined to almost $23 million, down significantly from nearly $66 million, the dip still exceeded analyst expectations. (The New York Times)

* Social curation network Pinterest is growing so rapidly that now it’s driving more referral traffic than Google+, Reddit, and LinkedIn combined. (GigaOm)

* According to an Amazon filing, daily deals site LivingSocial lost significantly more than it made last year: $558 million in losses compared with $245 million in revenues. (GeekWire)

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