Is Social Networking a Danger to Marraiges?

PostSecret put up a new batch of secrets today, and this was one of them. It got me wondering if social networking sites like Facebook and Myspace are hurting people's marriages. At one time, I kept hearing stories about people meeting men/women in chat rooms and eventually leaving their families to turn their cyber-relationship into a real one. But with Myspace and Facebook, people aren't usually just connecting with random, faceless strangers. They're REconnecting with old friends, colleagues and--sometimes--flames. Most of the time I'm willing to bet that the contact is innocuous. But as someone who communicates most effectively through writing, I know the power of words. One of my most intense relationships flourished over email before we ever spent time on the phone or getting to know each other face to face. How many people get a friend invite from an ex-boyfriend and girlfriend or maybe even an old crush? I read something a few years ago about high school love, especially if it was the first love, being so strong. Even though it's usually a totally different love than what we experience as adults, it still stays with us because it's our first experience. And when years pass and all you remember are the good times--and the times you had when you were much younger--seeing that old flame can drudge up a lot of nice memories. So the invite shows up. They add the person to their friend list, probably with no ulterior motives besides curiosity. They look through their pictures, read their profile. Then there's a comment here, a message there. Next thing they know, they're emailing back and forth with an old flame. At this point, it's probably still relatively innocent. But things happen. There's a fight with a spouse or a problem that the "ex" seems to understand better that the "current." Things get personal. Lines get crossed.

Is this far-fetched? Anyone else think that these sites could cause problems, even with good marriages? Anyone had experience with this? Feel free to post anonymously.