Have You 'Facebooked' Him?

By BROCK READ

Every time Tim Pittman logs on to Thefacebook, a Web site that displays photographs and short biographies of college students, he is linked to 120 of his classmates, friends, and acquaintances.

That can be a handy tool when he wants to fire off some quick e-mail messages, says Mr. Pittman, a sophomore at Harvard University. But it is only part of the site's allure. From his friends' profiles, Mr. Pittman can use the free service to link to more than 4,000 other students: casual