Before getting the 17-40L, I already had the 10-22mm EF-S and also the 24-70L. The 10-22 did not quite work for me, though. I would only occasionally need a wide angle shot (which, btw, would never be wider than 15mm) and even then I would find myself reluctant to switch to the 10-22 just for a single shot. So, I sold the 10-22 and got the 17-40L.
First impressions of the 17-40L - at 17mm, the sharpness is good corner to corner even at F4; at F8 the sharpness is simply amazing. At 28mm, central sharpness continues to be amazing but corner sharpness starts showing signs of deterioration. At 35mm the situation is still bearable and at 40mm things start falling apart. Central sharpness is still pretty good, though.
Compared to the 10-22 in the 17-22mm range, I find the 17-40L better. The problem with the 10-22mm is not its sharpness but its colors. Itís artificially contrasty, the colors look somehow enhanced but at the same time dull, so the image straight out of the camera ends up being kind of flat. The 17-40L has more natural and rich colors and I find the overall image quality to be much better. CA is slightly better controlled in the 10-22mm, though.
Compared to the 24-70L Ė at 24mm, the 17-40L is sharper at the center and slightly softer at the corners. At 40mm, the overall image quality of the 24-70L is better. CA is better controlled on the 17-40L than on the 24-70L.