In December, Facebook had more than 100 million more unique users than Google did when it went public in August 2004. In December 2011, Facebook had 162.5 million unique users in the United States. In August 2004, Google had 61.9 million U.S. unique visitors. It was a distant #4 among Web properties. (Yahoo was #1, with 113.1 million uniques.)
Strong usage can turn into strong demand among retail investors.
But for long-term prospects, it can also indicate saturation. At the time that Google went public, it reached less than 40% of the U.S. Internet audience. Facebook already reaches 73.7% of the U.S. audience.
For some reason, Google Docs charting starts the scale at 40 instead 0, this distorts the size of the difference between Facebook and Google. Facebook at IPO is 2.6x Google at IPO, but the chart makes it look 6x. Stranger still, I couldn’t find a way to get Google Docs to start the chart at 0.