This happened to one LJ user, when they accidentially payed LJ twice, and then revoked one of the payments via PayPal.
But it can get really sinister. You know that LJ stalker that's been bothering you? That asshat trolling your forum? Your exboyfriend? You have a vendetta against an LJ user? Especially one that's dedicated and has a permanent account, like myself?
Sign up a dummy account, and using that account, make a payment to your victim's account, as a gift. Then, contact your credit card company, say the payment was not made by you, and voila, your victim now loses their account. In the case of somebody who has purchased a permanent account, you're doing pretty decent financial damage.