During the past few years social networking Web sites such as Facebook and MySpace have exploded in popularity, especially with the 18- to 25-year-old crowd. Teens and young adults log on every day to see what friends have commented about on their page, posted new photographs or who's involved with whom. New teachers sometimes start their first jobs with profiles laced with pictures and posts illustrating late-night, college indiscretions - profiles some students may be able to view.