When trying to use the cards, they were declined and later informed that the card was closed. There seems to be a recent uptick in this activity, so keep a close eye on any Chase credit cards that you have.
So far, it's tough to say if this mostly affects Washington Mutual customers or if anybody with a Chase credit card is at risk. Wamu cardholders have plenty of complaints (see Wamu Cards Absorbed by Chase), but some longtime Chase customers have been fired as well.
I don't think there's a clear explanation why the cards were canceled. This is another sign of a scary environment where you should pay close attention to your credit, where you use your cards, and your monthly payments.