When your 88-year-old grandfather sends a request to be your "friend" on Facebook, you have two choices: Either confirm it, then quickly take down all those party pictures you thought were so funny, or plan on never coming home for the holidays.

...Social networking sites are still predominantly used by a younger population. The median ages of MySpace and Facebook users were 26 and 27 years old, respectively. At the career-focused LinkedIn, it was 40, according to a recent report by the Pew Internet & American Life Project.