I think you guys are both right. How early stage is FB is the golden question.

Here's Google's track record (since everybody seems to want to compare the two even though they're in entirely different businesses in theory). https://investor.google.com/financial/2003/tables.html

  Year    Revenue    %Growth
  2001    86m        352%
  2002    438m       409%
  2003    1.4b       234%
  2004    3.2b       118%
  2005    6.1b       92%
  2006    10.6b      73%
  2007    16.6b      56%
  2008    21.8b      31%
  2009    23.6b      9%
  2010    25b (est)  ~9%

Google was able to maintain growth doubling until 2006. Then the curve started to flatten out. Assuming FB is where Google was in 2003, they can grow. FB right now claims 500million users, but only about Google's 2003 revenue figures. In 2004, Google boasted they had 60million unique visitors. I'll leave the rest of the math up to the reader.