As someone who managed to get herself divorced twice before I had a Facebook account (and zero times since I've been on Facebook), I'm a bit skeptical.
Facebook is a social networking tool - nothing more. Before we had Facebook, we had MySpace, and before that Yahoo and AOL, and before that we had dating services, and before that we had the church and local dance clubs. People (married or unmarried) who have a mind to flirt have always somehow found a way to do it. But now, it happens on Facebook, because most of the civilized world is on Facebook.
If the divorce rate had dramatically increased since Facebook became popular, one could plausibly make a connection between the family breakdown and social networking, but the fact is that the divorce rate is down, both in the United Kingdom, and in the United States.
Perhaps instead of blaming Facebook for the divorces that are occurring, we should give Facebook credit for keeping more people at home with their spouses? That might also be an exaggeration, but Facebook does provide a tool (when used properly) to improve communication, which is important in a good marriage (or so I'm told).
Regardless, it seems like it would be wiser to pay more attention to what people are doing ON Facebook, rather than blaming the site, itself for the breakdown in any relationship (or the success of one).
Happy Friday, everyone - have a great weekend. Now, go hug your spouse if you still have one - good ones are hard to find.