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.
http://www.lensrentals.com/blog/2015/02/canon-11-24-f4-l-mtf-tests

$3,000?  Ouch.  It's a heavy beast too, at 41.6 oz.  My 10-22 EF-S weighs 13.6 in comparison, but I'd still love to have one.  The-Digital-Picture has a good bit of info about it here but no hands-on review yet.