I also would like to add my praise for this lens. I've used a variety of L lenses in the past (my favorites are the 85mm and 135mm primes), and this lens stacks up as equal or superior to the 16-35mm L. Images are preternaturally sharp -- I stopped taking pictures of my room because it kept showing how much dust there was on everything! I haven't had much chance to test out the color yet but initial pictures look promising.
I also have to plug the new and improved IS on this lens. I previously used the EF-S 17-85 as my primary lens, but this lens has vastly improved image stabilization -- I was able to get sharp shots at 0.8 sec shutter speed! Combined with the large aperture and wide focal length, this is a great indoor/night lens.