Canonrumors was our source for this, the first wedding shot on the currently unreleased Canon EOS-1D MKIV. Jeff Ascough was able to get his hands on a pre-release Canon EOS-1D MKIV and took it to a wedding he was shooting.
In his post, he's able to give some great information about his experience and there are quite a few stills too. Including one that shows the results at 100% of a shot taken at 1600 ISO and even one at 12800 to show the quality of the autofocus.
“As far as I am aware these are the first wedding images shot and published with the new camera anywhere in Europe, and possibly the world. Canon only allow a very select group of photographers to use their pre-production cameras, and I belong to that group – which I find very humbling.”
“I received the camera from Canon 24 hours before my wedding, and as this is a pre-production camera, I spent a good couple of hours checking and rechecking the camera to make sure everything was fine. I didn't have time to micro-adjust my lenses, but as it turns out I didn't need to. A few minutes into exploring the camera, I had everything set to how I like it, and I was away taking pictures.”
In Jeff's post, he asked other bloggers not to copy any of his images, and I will of course respect that request, so you'll need to go over there to see them.
(Photo credit: snap from Canon)