Or perhaps Mr. Market thinks it's a solid, say, $25 or $35 billion company that was just way overvalued at the IPO valuation of $100 billion plus. There's certainly a whole lot of commentary along those lines in the financial press, like this example from a few days before the IPO: http://marketday.msnbc.msn.com/_news/2012/05/15/11702548-is-...
That's certainly a defensible position: the company is stable and profitable as is, but the current valuation has a lot of growth priced in, which could only be realized by growing revenue per user substantially, and they haven't yet demonstrated how they're going to do that.
Mr. Market sounds pretty reasonable the way you describe him. But just 7 days ago he thought Facebook was worth 25% more than he thinks it's worth now. So he looks to me like the familiar Mr. Market portrayed in Benjamin Graham's book.
Seconded on the framing comment from lucianomt, and I'd also keep in mind that the people buying and selling 7 days ago were not the same people buying and selling now. At the IPO you had two special classes of participants. One the sell side: insiders and the underwriting investment bank. On the buy side: IPO speculators (i.e. people who specifically try to play IPO events, as opposed to people motivated by fundamentals and technicals).
On the technical side, the bulk of algo and technicals trading above a 1-2 day timescale would presumably not have been trading at the IPO. I'd venture a guess that these algo and technical traders provide the bulk of day-to-day price stabilization so their opinions matter, rightly or wrongly.
Ratio-driven fundamentals investors often look for, e.g. quarter-to-quarter metrics (changes in margin and so on), so they too lack the information to participate in their preferred manner until the next earnings report. I'd guess that the bulk of big pension and mutual funds operate in this fashion.
In short, the people transacting 7 days ago were not particularly representative of the market in general.
Graham doesn't think Mr. Market is always reasonable to begin with. But I'm not sure it's fair to attribute that valuation to "the market" as a whole. It was set by the underwriters, who might have been expecting a flood of "greater fool" buyers as in the late 1990s. They did exist (I'm sorry to say I know a few), but obviously not in sufficient numbers to generate the classic "pop"...
That's certainly a defensible position: the company is stable and profitable as is, but the current valuation has a lot of growth priced in, which could only be realized by growing revenue per user substantially, and they haven't yet demonstrated how they're going to do that.