Roger Cicala over at LensRentals has just completed optical benchmark testing of the Canon EF 11-24mm f/4L USM. You can read the entire article for detailed information, but the final few sentences sum up his findings quite well:
"This is a remarkable lens. Canon made the widest full-frame rectilinear lens available, and made it with superb image quality throughout the zoom range. Once again, hat's off to Canon's lens designers."B&H has the Canon EF 11-24mm f/4L USM available for preorder.