Our department put on an inservice training about how social networking sites can affect (ruin) your career. It is amazing how foolish people are on sites like facebook.
As a police officer, people would often ask to have their picture taken with you. Now, with the ability of photoshop to add to, or change, the photo's content, you don't dare allow these photos.
And yes, it is not uncommon for employers to require access to FB as terms of hiring. You don't like it? Apply elsewhere.