Underplaying it to the tune of $8B+ per year? Yeah, no sale.
If FB was really making that much money, why would they still be raising venture rounds (eg the Goldman investment)? If it was so the founder and early investors could take money off the table, why would they be undervaluing the sale? It would either be not smart for the founders or arguably misrepresentation to the investors.
I maintain my view that FB is still in the hype phase. Pricing will come back to earth at some point, which isn't to say it's not an $XX billion company but the $2B+ they've raised does raise questions about their actual and potential revenue.
Remember that Google raised $20-25M and that was it, as just one data point (but a common point of comparison).