The time-tested vow for married couples to stay together "until death do us part," is increasingly colliding with social media networks. One recent study of 5,000 divorce filings found that one in five lawsuits mention Facebook. Brad LaMorgese of Dallas-based McCurley Orsinger McCurley Nelson & Downing says Web sites such as Facebook provide wayward spouses an easy way to rekindle with former flames, while online communications create digital trails of deceit. And after a breakup, couples often tussle over who gets to maintain shared networks of online friends and acquaintances.

"Social media is becoming really relevant to our practice," says LaMorgese. "We see people trying to lock their spouses out of their online networks. We'll get discovery to see what they've done to their pages and find that they're posting updates about their new boyfriends or girlfriends while they're still married."

Writes Time magazine: Battles over finances and custody remain the Iwo Jima and Stalingrad of divorce cases. Opposing lawyers will press any advantage they have, and personal information on sites like Facebook, MySpace and LinkedIn is like decoded bulletins from enemy territory.

Half the fun of social-networking sites is the posting of personal news. The other half is the posting of personal opinion, something spurned spouses typically have in spades. MySpace and its ilk offer the giddying cocktail of being able to say something in the privacy of your home that will be publicly accessible, along with a chaser of instant gratification. All this at a time when people are often less than their best selves. On the walls of two Facebook groups - I Hate My Ex-Husband and I Hate My Ex-Wife, which together had been joined by 236 Facebook users as of early June - posts include all manner of (often misspelled) vitriol, including some colorful British slang: "my husband is ... a dirty smelly chavvy theivin alcoholic drug addict selfish scum bag" and "my ex wife is a no good lieing slag," each of which was posted alongside a smiling photograph of the commenter.