Do you think that social networking sites are responsible for a lot of relationship break ups?

I have just had another friend tell me of a couple who were together happily for over 10 yrs have now split because his partner was cheating on FB.

This is by far not the first time I have heard it, there seems to be a lot of people splitting up because of social networking sites. Whether they are cheating, flirting or just paying way too much attention to the computer and not their SO and the relationship.

So jellies whats your opinion? Do you know people this has happened too? Why do you think this is happening?