Yes another risk is the huge migration of online browsing to smartphones. It's a lot harder for Facebook to serve up ads on the small screen. It knows this and admits it does not have a fix yet. One solution might be to make people watch ads before they can proceed to their Facebook pages, a trick used by sites offering online video. But will Facebook users tolerate this?

And don't forget that Facebook competitor Google controls a big piece of the smartphone arena via its Android operating system, says Taulli. The search giant wants to be a bigger player in social media. Android looks like a pretty big potential weapon in the battle with Facebook over the use of social media on smartphones. "The Achilles heel for Facebook is mobile," says Taulli.

So far, Facebook has been great at facing challenges; it can probably figure out a way to overcome these risks, too. But the jury is still out.

Takeaway No. 5: Mark Zuckerberg is in the driver's seat

Facebook CEO Zuckerberg's portrait in the movies was not too flattering. And Facebook IPO filings suggest he's a control freak. He's lined up 57% of voting rights at the company through his stock holdings and alliances. This gives him total control over the company and its board, members of which would normally be picked by shareholders to represent them and help assure management does not do dumb things.

"It's just not shareholder-friendly," says Rudow. "It's not a good thing, because shareholders have absolutely no say."

Zuckerberg also has control over who runs the company after he dies, via prearranged instructions. This is pretty unusual.

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Zuckerberg owns a big stake in the company, so his interests are aligned with shareholders. But these slights toward shareholders have some investors wondering whether Zuckerberg, who has been ambivalent about his company going public, will be available to explain the game plan when problems crop up.

If he doesn't interact with investors often enough in person, they can always try messaging him on Facebook.

At the time of publication, Michael Brush did not own or control shares of any fund or company mentioned in this column.

Michael Brush is the editor of Brush Up on Stocks, an investment newsletter. Click here to find Brush's most recent articles and blog posts.

Stocks and funds mentioned on previous pages include Google (GOOG, news), Apple (AAPL, news), John Hancock Balanced A (SVBAX), Goldman Sachs Group (GS, news) and Morgan Stanley (MS, news).