One of the Benz executives was interviewed last year regarding the 2011 facelift. According to what he said, everything from the front bumper to the start of the windshield was modified. (Well, and the engine. I think even the CL550 has a twin turbo now?) If you look at pre-2011 and 2011+ from the front, even the hood has a different shape. The AMG versions are even more different, and make the facelifted versions look pretty similar to the new CLS.
Interestingly enough, when I was looking around for custom grilles a few days ago, I found a pre-2011 conversion kit on ebay that makes 2010 and earlier CLs look like a 2011/2012 AMG. Lights & everything, I think? Hood is the same shape though.
http://www.ebay.com/itm/07-08-09-10-...item35a6cd6e20