Go ahead, call it an obsession. But chances are, if you're a college kid with a bunch of friends, a lot of work to do and a computer with Internet access, then you're logged onto thefacebook.com. The website, created by Harvard kids for Harvard kids who wanted to visualize their social network and determine their overall importance in the college circle, now boasts more than 3 million users on hundreds of campuses. Students create personal profiles, post photos (some of them pretty raw, like the SMU swimmer clothed in nothing but a big smile) and hook up via online invites. Facebook is a dream for its creators and a nightmare for curious students who can't stay logged out long enough to finish that history paper.