Unable to sell their private shares, Facebook employees are growing restless, and according to Kate Kelly at CNBC, an initial public offering is expected in the first quarter of 2012. Kelly reports, "A factor in the company's IPO timing is the Securities and Exchange Commission's requirement that some companies like Facebook must disclose financial information if they have more than 500 private investors." The latest IPO speculation and record high valuation is prefaced, however, by a mixed bag of recent numbers showing flagging usership in some of Facebook's top markets.

Just over a year ago, Mark Zuckerberg said in an interview that user anxiety over privacy settings would wane. Like they did with the introduction of the News Feed in 2006, a bunch of users would complain but would eventually come around to realize that the social network's more open approach made for a better Facebook experience. At Europe's e-G8 forum, the company's founder responded to questions about the flak Facebook received after a flurry of controversy over new privacy settings and Zuckerberg saying he "doesn't believe in privacy." But the users would prevail, the young CEO said. "One of the good things about the Internet is you can just kind of build something, and people will choose to use it or not."

In the past year, millions of Americans have chosen not to use Facebook. According to numbers reported on Inside Facebook, the social network is inching towards the 700 million user mark with loads of new sign-ups in many countries late to adopt Facebook but growth has slowed over the past two months in the United States. Why? Fewer Americans--as well as Canadians, Brits, Norwegians and Russians--are signing in:

Most prominently, the United States lost nearly 6 million users, falling from 155.2 million at the start of May to 149.4 million at the end of it. This is the first time the country has lost users in the past year. Canada also fell significantly, by 1.52 million down to 16.6 million, although it has been fluctuating around that number for the past year. Meanwhile, the United Kingdom, Norway and Russia all posted losses of more than 100,000.

The quick answer to why growth is slowing would have to be saturation. It's no surprise that interest would have peaked by now for Facebook's oldest market . ZDNet's Larry Dignan writes, "In other words, you could go into a football stadium ask everyone without a Facebook account to raise their hands and you’d be lucky to get a dozen people without an account." Further, Inside Facebook's Eric Eldon says the slowdown is to be expected, "By the time Facebook reaches around 50% of the total population in a given country (plus or minus, depending on internet access rates in that country), growth generally slows to a halt."

But why the dip in activity? (Eldon's numbers depend on monitoring an advertising tool that registers the how many users actually sign into the service, on a daily basis.) A year before that The New York Times reported on the social network diminishing cachet. In making sense of the "Facebook Exodus," The Times's Virginia Heffernan talked to a once prolific user who talked about her switch to Twitter over Facebook. "Facebook is good for finding people, but by now the novelty of that has worn off, and everyone’s been found." A year later, around the time Zuckerberg was talking about users choosing or not choosing to participate, campaigns to quit Facebook--many citing privacy concerns--appeared across the country. Meanwhile, Twitter has boasted tremendous growth, both in new sign ups and daily activity.

Whether Americans are getting bored of Facebook or angry about privacy invasions apparently matters little to the would-be trillion dollar company. TechCrunch's Robin Wauters says we obviously live in "a Facebook world" when you look at traffic data from the past two years. Flagging in U.S. numbers may slow growth, but the network's not going anywhere. Look at all the blue:

Mark Zuckerberg, now maybe engaged, sounded inspirational if unflagging, when he spoke at an eighth grade graduation in Silicon Valley last week. "It’s not about a single moment of inspiration or brilliance, it’s years and years of practice and hard work, " Zuckerberg said. "Anything that’s really awesome takes a lot of work."