A little story, with two halves.
First half: One of my roommates is somewhat disorganized. After holding a check of mine from June to mid-October last year before cashing it, we came to an agreement. He would have two weeks to cash checks written to him, or would eat the cost. I'd typically write "VOID AFTER (date)" and give him to the end of the month.
Second half: WAMU lets certain companies do direct debits from checking accounts, regardless of whether the customer has authorized them to do so. For example, SDG&E and Time Warner. This has always irritated me, because I don't get the checks back and I can't even see the check image online. All I get is the number, and there's no paper trail.
Putting it together: February 3rd I wrote the roommate a check for my portion of the cable and phone bill-- $22.45-- and wrote "VOID AFTER FEBRUARY 28th, 2007" in big letters up on the top. Sometime mid-March I wrote off the debt. May 21st a charge appears on my account: "TIME WARNER-SAND CHECK PYMT (number)" for $22.45.
Well, it turns out the roommate had accidentally mixed up checks sent to the cable company-- and they cashed it! Not only was it not made out to them, but it was void three months prior! But the charge went through, because nobody at WAMU actually verified anything.
Moral of the story: if you want perform invalid transactions, forge checks, or other illegal behavior, Time Warner is happy to launder your money.
And the roommate's actually going to refund me the dough so I'm not going to go bitch and moan at the companies involved here-- although it would be interesting to try and track this all down.