The newest scare story sweeping the Internet is the idea that Facebook breaks up marriages, by facilitating infidelity. It's perfectly coherent to believe that there's been some kind of infidelity-increasing technological shock but statistics like "[m]ore than a third of divorce filings last year contained the word Facebook" and "over 80% of U.S. divorce attorneys say they’ve seen a rise in the number of cases using social networking" don't really prove the case.
After all, it's also the case that there's been a huge surge in recent years in marriages between partners who used a strategic decision to "friend" one another after meeting as an early sign of romantic interest.
Facebook didn't exist ten years ago, and it's very popular now. So for all forms of human interaction, including infidelity and divorce, there's been a huge increase in Facebook-related forms of interaction. But that'd be like saying shirts cause murder because almost all murderers wear shirts. When technology becomes ubiquitous that can have wide-ranging implications for society. But it can also have completely trivial ones.