ISO have posted the official news to their web site, and the less than inspiring title, "ISO/IEC DIS 29500, Information technology – Office Open XML file formats, has received the necessary number of votes for approval as an ISO/IEC International Standard."
I’ve had some pretty robust things to say about certain competitors who used approval by standards bodies as a substitute for producing a good product, and the temptation to go "Nah nah na-na nah" – or something equally childish is pretty strong. But that would be to ignore a couple of important things, the first is Microsoft handing over responsibility for file formats to a standards body. The second is that customers get both choice of file formats and the comfort that Microsoft (and others) won’t go changing standards on a whim.
Brian Jones has a very well thought out post on the subject if you want to read more.