According to a British legal website, Facebook is cited in one-third of divorce filings:
Facebook is becoming a major factor in marriage breakdowns and is increasingly being used as a source of evidence in divorce cases, according to lawyers.
The social networking site was cited as a reason for a third of divorces last year in which unreasonable behaviour was a factor, according to law firm Divorce-Online.
The firm said it had seen a 50 per cent jump in the number of behaviour-based divorce petitions that contained the word ‘Facebook’ in the past two years.
[…]
The most common reasons for Facebook causing problems in relationships were a spouse finding flirty messages, photos of their partner at a party they did not know about or with someone they should not have been with.
I prefer to think people are filing for divorce because their spouse won’t stop sending them requests to play “Hidden Chronicles.”
It’s amazing how much social media is being used in family law. In Australia, it’s estimated that photos/comments from social media are being used to discredit people in 20% of Family Court proceedings. In the UK, a spouse’s behaviour on Facebook is now cited in a third of UK divorces in which unreasonable behaviour was a factor. Unfortunately, social media’s impact on family law does not stop there – as it’s also now a major tool for divorce-related bullying (e.g. continuing communication, posting nasty messages, hacking accounts, etc). More: Family & The Law (Family Law Portal)