Michael Smith gets teased on a weekly basis by his friends for a personal decision he made two years ago.

While most people in Mr. Smith's generation use popular social networking tools such as Facebook and Twitter, the 29-year-old from Chattanooga refuses to join any online social network.

"You're considered an outcast if you don't have a Facebook account," he said.

Mr. Smith may be in the minority but he is not alone in his criticism of social networks including Facebook and Myspace.

While 70 percent of all 18-29 year olds in America say they use a social networking site, about 25 percent of that age group think sharing personal information through those networks is a "bad thing," according to a study the Pew Research Center for the People and the Press released in May.

In response to the popularity of social networks, some researchers -- including Steven Seiler, a sociology doctorate student at the University of Tennessee at Knoxville -- are beginning to study what kind of long-term effects this type of communication has on society.

For four years, Mr. Seiler has been studying the effects of communication including online social networks on people. He says users in the 18-29 age group no longer distinguish reality from online networks.

"We're half way in a digital space and half way in a physical space," he said.

Mr. Seiler said he is finding patterns in people who criticize such networks, and a common reason is they want to keep their lives private and maintain control over their own accessibility.

When surveying University of Tennessee students, Mr. Seiler found users associated what happened on Facebook the same as their physical situations, such as when a friend didn't respond to a wall post or instant message quick enough they thought they were being ignored.

Being connected through social networks produces the assumption that everyone is always available and causes people to expect accessibility, he said.

People have realized that Facebook and other social networks can have positive effects, including "strengthening ties you already have" and allowing you to meet new people, said Dr. Suzzane Kurth, a University of Tennessee sociology professor.

But a growing group of young people are beginning to realize the effect of having a "written record" in public, she said. And she found more of her students were not investing as much time into adding status updates and pictures to their Facebook pages.

"(Facebook) is still in a growth faze," she said. "Over time (people) might be more cautious of what they put (on their site)."

As some people continue to post private and often times crude pictures and status updates, one Web site called Lamebook pokes fun at people who use no discretion. The site claims its purpose is to "post lame and funny pictures, status updates and other gems found on your favorite social networking site."

But Mr. Seiler said many users don't have boundaries online, and people he surveyed seem to have mixed emotions about the positive and negative effects from online networks.

In the meantime, Mr. Smith said his friends don't understand why he stays away from Facebook, and he is flooded with e-mails suggesting he join the ranks.

"When did we become so concerned with someone else's status? Three years ago would you have called me every hour?" he said. "Why do you need to tell everyone what your doing?"