Half of Americans think Facebook is a passing fad, according to the results of a new Associated Press-CNBC poll. And, in the run-up to the social network’s initial public offering of stock, half of Americans also say the social network’s expected asking price is too high.

The company Mark Zuckerberg created as a Harvard student eight years ago is preparing for what looks to be the biggest Internet IPO ever. Expected later this week, Facebook’s Wall Street debut could value the company at $100 billion, making it worth more than Disney, Ford and Kraft Foods.

That’s testament to the impressive numbers Facebook has posted in its relatively brief history. More than 40 percent of American adults log in to the site —to share news, personal observations, photos and more— at least once a week. In all, some 900 million people around the world are users. Facebook’s revenue grew from $777 million in 2009 to $3.7 billion last year. And in the first quarter of 2012 it was more than $1 billion.

Just a third of those surveyed think the company’s expected value is appropriate, 50 percent say it is too high. Those who invest in the stock market are more likely to see Facebook as overvalued, 58 percent said so. About 3 in 10 investors say the expected value of shares is fair.

But price worries won’t necessarily stop would-be investors. Half the people surveyed say they think Facebook is a good bet, while 31 percent do not. The rest aren’t sure. Americans who invest in stocks roughly agree, although investors who are more "active" — those who have changed their holdings in the past month —are more negative. Nearly 40 percent say Facebook would not be a good investment.

Young adults, a majority of whom log on to Facebook daily, are more willing to dance to their hoodie-wearing piper, 28-year-old CEO Mark Zuckerberg. Among Zuckerberg’s peers, adults under age 35, 59 percent say Facebook is a good bet. Compare that to the views of senior citizens: Only 39 percent age 65 and over say Facebook shares are a good investment. Nearly half of Gen X’ers (ages 35-44) say the company is a good bet, as do 55 percent of middle-aged people.

Those under 35 are the generation most interested in Facebook’s IPO because they’ve grown up immersed in the social network. They were the first users, logging in from their college dorm rooms. Later, Facebook expanded to allow high school-age and even younger students to sign up. It’s become an integral part of their lives, giving them a launching pad to spread the news of life’s major developments through posts and pictures.

Conversely, it’s the rare senior citizen on Facebook: Just 21 percent have an account. Half of baby boomers — the generation born in the years after World War II — have one. But most of the 56 percent of the country that’s on Facebook is young — two-thirds of Gen X’ers and a staggering 81 percent of people 18-35 use the social networking site.

Young people aren’t just connected. They are constantly tethered to smartphones, tablets and notebook computers. Even with the rise of alternative social networks like Twitter and Google Plus, 55 percent of Zuckerberg’s peers go on Facebook every day. A third log on several times a day. Despite the intensity of their use, a narrow majority of young adults predict Facebook’s appeal will fade down the road (51 percent), fewer think it will stick around as a service (44 percent).

The public overall is similarly divided on the company’s future. Just under half of adults (46 percent) predict a short timeline for Facebook, while 43 percent say it has staying power.

Young people are more aware of Zuckerberg and have more positive views of the CEO, who celebrated his 28th birthday on Monday. Overall, one in five Americans say they’ve never heard of him, 30 percent don’t have an opinion and 14 percent plain don’t like him. Only about a third have a good impression of the CEO, who has alienated some with Facebook’s ever-changing approach to user privacy.

But 46 percent of people under 35 like him. And a scant 4 percent of those younger adults say they’ve never heard of him.

The privacy issue is a stinger. Three of every five Facebook users say they have little or no faith that the company will protect their personal information. Only 13 percent trust Facebook to guard their data, and only 12 percent would feel safe making purchases through the site. Even Facebook’s most dedicated users are wary — half of those who use the site daily say they wouldn’t feel safe buying things on the network.

As for how Facebook makes most of its money —selling ads— 57 percent of users say they never click on them or on Facebook’s sponsored content. About another quarter say they rarely do.

Despite user discontent about privacy, Facebook and Zuckerberg have connected with many Americans. The survey suggests that his reputation and youth seem more like assets than liabilities. For those who have heard of the CEO, two-thirds are at least somewhat confident in his ability to run a large public company. Twenty-two percent doubt he can handle the leadership role. As for the social network he created, 51 percent of Americans clicked "Like."

The Associated Press-CNBC Poll was conducted May 3-7, 2012 by GfK Roper Public Affairs and Corporate Communications. It involved landline and cell phone interviews with 1,004 adults nationwide and has a margin of sampling error of plus or minus 3.9 percentage points.