New research into Twitter usage uncovers some surprising facts about who's on the much-hyped social network and how they're using it.Earlier this week, at Twtrcon '09 in San Francisco,

the Participatory Marketing Network (PMN) release the results of a study conducted in partnership with Pace University's Lubin School of Business.

Unsurprisingly, the study found that 99 percent of consumers between the ages of 18 and 24 (so-called Generation Y) had active profiles on at least one social networking site.

More surprisingly, only 22 percent of the same group said they used Twitter. Of those, 85 percent follow friends, 54 percent follow celebrities, 29 percent follow family, and 29 percent follow companies.

"This is a classic 'glass half full' scenario for Twitter because it’s clear that Gen Y has an appetite for social networking, but still hasn’t fully embraced micro-blogging," said PMN co-founder and executive chairman Michael Della Penna.

From the point of view of a marketing firm, the study is a sign that there's a huge opportunity in getting that group more active on Twitter.

But with mobile devices and texting dominating Gen Y's social networking activities (the study found that 38 percent have an iPhone or iPod Touch), the question has to be, what's Twitter's attraction for that group?

Especially in light of another recent survey that found that Twitter has become more of a broadcast medium than a true network of peers.

A review of the activities of 300,000 Twitter users conduced by members of the Harvard Business School found that 10 percent of Twitter users accounted for more than 90 percent of all the tweets.

By comparison, other social networks are more democratic: the top 10 percent of users account for just 30 percent of all the content.

The researchers cited Wikipedia as an online venue with a similar pattern of usage: on Wikipedia, 15 percent of the editors account for more than 90 percent of the content.

"In other words, the pattern of contributions on Twitter is more concentrated among the few top users than is the case on Wikipedia, even though Wikipedia is clearly not a communications tool," the researchers concluded. "This implies that Twitter's resembles more of a one-way, one-to-many publishing service more than a two-way, peer-to-peer communication network."

In addition, most Twitter users barely participate at all. The median number of lifetime tweets per user is one, while 75 percent of users have tweeted just four times.

The Harvard researchers discovered some other insights about Twitter usage. Unlike most social networks, where women provide most of the activity, tweeting men have 15 percent more followers than women, even though women represent 55 percent of the service's members.

In addition, men are more than twice as likely to follow another man than to follow a woman, while women are 25 percent more likely to follow a man than a woman.

A venue in which a few contributors, mostly men, dominate the conversation doesn't sound like much of a social revolution. That may help explain last month's report that only 40 percent of U.S. Twitter users return the next month.