An interesting document to print and save: the Facebook's filing for its initial stock offering of $5 billion. It is here, on the SEC's Website.

This is my summary:
 

1. The vast majority of revenues (85 percent) came from advertising. Also proceeds come from virtual good sales on Zynga (12 percent).
   
   Facebook reported $3.71 billion in revenue in 2011, and $1 billion in profit.
   
   An advertiser could reach an estimated audience of more than 65 million U.S. users in a typical day on Facebook.
   
   Big ad spenders are Netflix, with $3.8 million in 2011, and the Washington Post Company, $4.2 million.
   
   Facebook "is the most ad-dependent old media firm, more dependent on ad revenue than CBS," writes an analyst at Thomson Reuters.
   
    
2. "We compete broadly with Google's social networking offering, including Google+, which it has integrated with certain of its products, including search and Android."
   
    
3. "Like" addition Facebooks users generated 2.7 billion likes and comments a day in the last three months of 2011.
   
    
4. Half of its 845 milion monthly active users log every day. 
   
   In Japan and South Korea, Facebook has a penetration rate of less than 15 percent. In China, where Facebook access is restricted, it has 0 percent penetration.
   
    
5. Facebook has built storage and serving technologies, like Haystack. Facebook stores more than 100 petabytes of photos and videos.
   
   In 2012, the company will spend $1.8 billion in servers, network equipment, storage infraestructure and the construction of data centers.
   
   It owns a data center in Prineville, Ore., and in North Carolina. Facebook leases facilities in California and Virginia.
   
    
6. Paychecks: Sheryl Sandberg makes $381,966 a year. Mark Zuckerberg's salary is $703,833, but he owns 28.4 percent of the company.
   
    
7. Venture capitalists: Accel and DST own at least 5 percent of the company. Below 5 percent: Goldman Sachs, T. Rowe Price, Kleiner Perkins Caufield & Byers, Greylock Partners, Elevation Partners, Tiger Global, Meritech Capital Partners, Li Ka Shing and Andreessen Horowitz.
   
    
8. Risk factors Facebook cites: changes in user sentiment, adopting privacy policies perceived negatively, adverse media reports, inability to present meaningful information to users, overwhelming users with ads, government regulation, cyberattacks with malware, viruses and computer hacking.
    

The New York Times wrote an extended report about it.