http://www.imaging-resource.com/PRODS/E7D/E7DA3.HTM
Canon has eliminated the air gap between the LCD and cover glass by sandwiching a special optical elastic material between the LCD and the cover glass. This optical elastic material has the same high refractive index as the glass itself. The cover glass is also a reinforced glass instead of the acrylic used on the 50D, so they also eliminated the special anti-reflective and scratch-resistant coatings found on the other recent EOS cameras. The appearance of the LCD is reminiscent of instruments like a liquid-filled compass, with added contrast and less glare. Better yet, it doesn't give your images a blue cast that makes color harder to judge, especially when outdoors with the 50D.
Again, it's a nice little evolutionary change but nothing dramatic. In practice, the only time you might see a difference is in bright sunlight, but keep in mind that the 7Ds screen isn't perfect in those conditions either.