Google's annual display ad revenue from Double Click is only $5 billion + they have $32 billion of additional revenue sources. That means if Google only had the display ad business similar to Facebook their valuation would be 1/8 or less or around $25B. Here is the scary part when you start to look at Facebook's proposed IPO valuation of $100B with 88% of its revenue coming from one source.
Facebook simple valuation equation based on current estimates:
Google Market Cap = $188B at $580 per share
Google Total Annual Revenue = $37B
Google Display Ad Revenue = $5B
Facebook Market Cap = $100B
Facebook Total Annual Revenue = $5
Facebook Display Ad Revenue = $4.8
Facebook Fair Value Equation = ($37 / $5 = .135) x $188 = $25B
The latest news sources reported that Facebook annual display ad revenues were around $3.8B in 2011 and so I will assume this revenue number has grown to $5B in 2012. $5B in annual revenue for Facebook is 1/8 the the size of Google's with $37B. Facebook has 88% of its revenue coming from display ads only which is not very diversified if you ask me. Keep in mind this does not factor in growth rates but they cannot be that dramatic to change my valuation estimates.