1. For example, CU Community, which began at Columbia University, had an early head start. See http://www.slate.com/id/2269131/. This account of Facebook's founding is drawn from David Kirkpatrick's The Facebook Effect (New York: Simon & Schuster, 2011).
2. Actual engagement numbers from 2004 are hard to find, but this pattern has been consistent throughout Facebook's public statements. For example, Chris Hughes reported in 2005 that "60% log in daily. About 85% log in at least once a week, and 93% log in at least once a month." http://techcrunch.com/2005/09/07/85-of-college-students-use-facebook/
3. I first heard the term leap of faith applied to startup assumptions by Randy Komisar, a former colleague and current partner at the venture firm Kleiner Perkins Caufield & Byers. He expands on the concept in his book Getting to Plan B, coauthored with John Mullins.
5. "A carefully researched table compiled for Motor magazine by Charles E. Duryea, himself a pioneer carmaker, revealed that from 1900 to 1908, 501 companies were formed in the United States for the purpose of manufacturing automobiles. Sixty percent of them folded outright within a couple of years; another 6 percent moved into other areas of production." This quote is from the Ford biography The People's Tycoon: Henry Ford and the American Century by Steven Watts (New York: Vintage, 2006).
6. Jeffrey K. Liker, The Toyota Way. New York: McGraw-Hill, 2003, p. 223.
8. In the customer development model, this is called customer discovery.
9. For more on the founding of Intuit, see Suzanne Taylor and Kathy Schroeder, Inside Intuit.
10. For more on the Lean UX movement, see http://www.cooper.com/journal/2011/02/lean_ux_product_stewardship_an.html and http://www.slideshare.net/jgothelflean-ux-getting-out-of-the-deliverables-business