I agree that some of the Canon wide angle lenses are not all that I could hope for. Yet in careful tests with 16-35 series I lens on both he 5D and 5DII - at 16mm f8, I see a bit more detail in the 5DII files. The same is true of the 24TS-E. So shooting with these lenses and the others that I own is still better on the 5DII than on the 5D. I expect the new 17 and 24 TS-E lenses to be a lot better, or what is the point of them?
Alan, check out the 16-9 shoot-out between the Canon 17-40, Nikon 17-35, and the legendary Contax Zeiss 21mm. In the center at f/11, where a lot of people seem to think the 17-40 is at it's best for landscape work, the 17-40 is essentially the equal of the Zeiss in resolution and there's only a little falloff away from center (at 100% magnification).
At f/16 the 17-40 is within a point or two of the Zeiss in terms of resolution edge-to-edge and has much less geometric distortion. In fact, Welsh says that if you correct for distortion then the Zeiss produced images are "scarcely better" than the Nikon or Canon. Yes, Welsh notes that the Zeiss has a little more contrast and sparkle (again if you don't correct), but this is still pretty amazing stuff, and strongly counterbalances, at least for typical landscape photography apertures, the "all Canon wide-angles suck" school of thought.