AnandTech reviews 5D MkII resolution & noise
 

You can check out the review and images here:
AnandTech: First Look: Canon 5D Mark II

The bottom line is that the 21MP 5D MkII matches the low light noise of 12MP cams at high ISOs, and beats the 24MP Sony A900 pretty solidly.

This is a quick review of a production model, and it doesn't even mention video. One commenter mentioned video though - and they had a stuck pixel. Ouch. You can clean up a pixel when needed on a still, but it would be no fun on video. To have to apply a one pixel effect to clean up EVERY CAPTURE OR LAYER would be a real pain.

Flickr Photo Download: 5D mkII stuck pixel

The reason the A900 looks so terrible is this:

The A900 JPEG engine is terrible. So while it's fair to say the 5d2 beats the A900 at making jpegs, they are much closer in raw files (with only a slight edge to Canon).

I was wondering about that. It'll be interesting to see how the RAW images compare.

In any case, its good to know that the 5D2 has a nice JPEG engine, though I don't expect to use it much. With video, having straight 1080 vs RAW might have a workflow advantage, but for stills, I expect to scale, crop and fine tune virtually every image I shoot, so RAW is fine by me...

Its very easy to fix hot pixels on video... actually as easy as fixing them in stills...

I think I also read that he later did some clean routine and the hot pixel was gone???