Well, we're still at the very early stages of social media on the web. As someone else points out in another comment: owning the complete social graph may very well be the most valuable asset ever. I think the potential market for Facebook can grow much more than just 3 times over the next 7 years.
Inflation has been low the last decade, but sure, that affects the numbers.
Social media is a nonexistant. It's something somebody at Facebook (or Twitter) dreamed up to hype and justify existence.
From henceforth I declare this movemenet DuncanIdahia - you may not have heard of us - but we're growing tremendously (we grew infinitely from 5 minutes ago to now).
Based on these numbers, if you think Facebook is overvalued today you sort of have to make the same conclusion about Google in 2004.
In fact, Facebook has even higher profit than Google did when it was valued the same.