What are they doing? Increasingly, spending time on Facebook.com , a popular Web site that allows users to put in some face time without even leaving their rooms.

"I log in about five times a day," says Renee Grassi, a student at Marquette University, who initially resisted joining the social network for students because, she says, "I didn't want everyone knowing my business."

A member of the site for about two years, she is among more than 8.6 million people who, for any number of reasons, post a picture and some "facts" about themselves and their favorite things on their profile page.

Facebook was created about 2½ years ago by former Harvard student Mark Zuckerberg so that college students could network, using their e-mail addresses from participating universities. Now it is open to many high schools, military bases and even some corporations.

Members post information about themselves such as favorite movies and quotes, along with personal information such as phone numbers and a preferred e-mail address. Users are then able to see other profiles of people in their network - but only if they are invited as "friends." People outside of one's personal network can view information only after being added as a friend and if one's privacy settings correspond with their level of "friended-ness."

Facebook weathered a tsunami of user protests this month after introducing a pair of new tools, News Feeds and Mini-Feeds, which tracked and streamed information about the site-related actions of users and their Facebook friends.

"We didn't build in the proper privacy controls right away," founder Zuckerberg wrote in an open letter to Facebook members dated Sept. 8 (snipurl.com/wezv). Zuckerberg's letter explains the privacy concerns of some users and Facebook's efforts to address them.

The ability to control how much information is available to the public is one of Facebook's core principles. According to Facebook's privacy policy, "People should have control over their personal information, and they should have access to the information others want to share."

It's this feature, among other things, that separates Facebook from other, similar sites such as Myspace.com, which lets anyone join and look at profiles of other users. Though there is a privacy setting on Myspace, many people don't seem to be aware of the feature.

"I had a Myspace account, but I never did anything with it because anyone could look at it," says Ashley Schertz, a Ripon College student. "It kind of creeps me out."

Schertz, who plays on the college volleyball team, uses the privacy settings to keep some of her profile information from younger girls she coaches.

Alysha Schertz, a student at Carroll College in Waukesha, is on Facebook, too, with a profile that is set up so that only friends can see it. That makes her feel safe enough to put her e-mail address and cell phone number up.

Justin Smith, who follows the social networking phenomenon and writes a blog called "Inside Facebook," sees the site as a "less awkward" option of talking to new people.

"I like Facebook for the fact that I have friends who go to school in California and Washington and all around the country," says Rajeev Chaudhary of Mequon. "I can talk to them, and they can respond really fast."

A student at the University of Wisconsin-Madison, he started using the site more than a year ago, as soon as he had a college e-mail address and before he graduated from high school. He met some of his dormmates through Facebook before he left for college.

"I accepted them as my friends on Facebook since I'd be living with them," says Chaudhary, referring to the process of allowing greater access to Facebook information he has posted about himself. He usually accepts friend requests unless there is no chance that he knows the person.

Though the site makes it very simple to keep in touch with friends close by or in far-flung places with its public messaging on profile walls - or private messages that can be sent on a cell phone - it doesn't make deep connections any easier.

"It keeps me in touch with a lot of high school friends who I probably wouldn't talk to on the phone," Ashley Schertz says. "But if I need to talk to my sister, I usually call her on the phone."

Frequent users say one reason for Facebook's growing popularity is that it provides a sense of belonging and connectedness, which helps define someone's identity. Facebook users join groups, some based on real-life organizations and some not.

Some Facebook members might join a group related to a club at school, for example, such as student tour guides or the marching band. Other groups may be related to political beliefs, sports teams, vegetarian beliefs or some piece of pop culture, such as Phish or Keller Williams fans.

Among the clever group titles are "Advocates of the Nap," "People Who Miss Their Pets," "Ozaukee County: the Real O.C.," "I'm To Good for Grammar" and "The Paper I'm Typing Is Due Right About Now." There are thousands from which to choose.

Grassi, the Marquette University student who was reluctant to join Facebook because she wanted to keep her private life private, is a member of "People Who Swore They Would Never Join Facebook."

By using registered e-mail addresses, Facebook users are attached to their real-life identities, but that doesn't mean everything posted necessarily is a fact.

Take the "Relationship Status" feature. Members can choose between "Single," "In a Relationship," "In an Open Relationship," "Engaged," "Married" or "It's Complicated." Chaudhary, the sophomore at UW, says, "Apparently, these days a relationship's not official unless it's on Facebook."

But just as relationships can be confirmed, their existence can be denied. Ashley Schertz, who is in a relationship both on Facebook and in real life, recalls, "My roommate had been dating this guy, and he wouldn't accept her invitation" to be one of her friends on Facebook.

Once thought of as only a student connection, Facebook is reaching beyond the high school and college years. Military bases are becoming part of the network, and Facebook started adding corporations in May.

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