Layperson question: what does it matter? What impact does Facebook's valuation have on its day-to-day business, now that they have the IPO cash in hand?
That being said, Facebook doesn't actually need the cash for anything (apparent). It is profitable and can hire and build data centers.
For a company in Facebook's position, any large cash pile is likely to be used for acquisitions more than anything else.
But the share price still matters. It affects the company's ability to attract and retain talent.
In the 90s Microsoft did amazingly well from this. IIRC at the time an employee's stock options were price at the lowest closing price in the month after they joined. This meant that someone who joined in around 1990 could buy MSFT at less than $1 when it was trading at 50-100 times.
It is very hard for someone to leave in that kind of position.
AFAIK option vesting and pricing has changed somewhat since then (typically with the whole 4 year vest and 1 year cliff) such that early employees are probably fully-vested. Later share parcels won't be anywhere nearly as attractive. So those employees will stay basically as long as it's fun because it's not about the money anymore.
Then again, good luck motivating such people to do shitty jobs.
Facebook is now (IMHO) beyond the point where stock can be considered a lottery ticket anymore. Even it becomes a trillion dollar company that's still only 10x. At this point, a potential employee can simply multiply his or her RSU (restricted stock unit) allotment by the current price divide it by the vesting period and add that to base compensation plus target bonus to work out total comp.
Zuck still holds 57% of the voting power in Facebook so really the stockmarket doesn't matter much at all to Facebook. It's still Zuck's company and he can (within reason) do what he likes with it. That seems to be a tech company norm and probably a good thing based on the short-term narrowsighted thinking that seems to dominate Wall Street (just look at Yahoo).
TL:DR effect on FB = not a lot.
[1]: http://online.wsj.com/article/SB1000142405270230344840457740...
In FB's case however, Zuck still controls (through proxy) the majority of votes; Zuck cannot be ousted.
There are other problems with a non-performing stock too; employee morale may be (and is increasingly?) tightly related to the share options they own. If management is not performing well and costing their employees money (!) that can ruin morale.
This doesn't just involve Facebook; currently the market is pretty bullish on web companies. It can quickly turn bearish, restricting the capital that currently flows so free.
With high level share liquidity, insiders will find it easier to cash out and walk away from Facebook. Particularly those that have been there for a long time. The market has set a 'real' price on the shares, whereas the Second Market pre-IPO trading was a lot less liquid, and made it difficult to guess just what FB's real value was. Now employees know what their shares are really worth on a durable time frame.
The stock market is in a down swing, so there was little chance FB was going to see a healthy pop today. If you're building a long term business, all of the talk about it being up or down or popping today is literally irrelevant.
Groupon is specifically a great example of the investor con-game that goes on. They IPO'd a near historically small float (for a large company) to get as big a pop out of the stock as possible to punch the valuation high. Smoke and mirrors, and the stock proceeded to collapse 62% accordingly. It's a good sign that Facebook didn't pull any of that shit, and by all indications had a very sane and orderly IPO process.
If you're interested in the stock, give it time, you'll be able to get it under $30 / share in the next year.