On December 7th, 2005, Mark Zuckerberg joined CS50 for a guest lecture about Facebook and computer science. When you watch the video, take a look at just how many people showed up (perhaps less than 10 in an the entire auditorium). Pay close attention to how Professor Michael D. Smith introduced Zuckerberg and the idea of his startup. How things change.
Later on in the video, Zuckerburg mentions that Google sees 250,000 page views, yet Facebook's count is 400,000. His analysis on how Facebook is able to serve this much content with such a small team (50 at this time vs. thousands at Google) is interesting to note as well.
I'd suggest listening to this like you might listen to a podcast. Questions asked by the audience are sometimes difficult to make out, but still worthwhile.