When I bought my 40D, I never really consider the 16-35 due to its price. Shooting 17-40 on a cropped body eliminates the softness on corners, and 3 years using it with my 40D left me without much complains at all. After all, I saved the extra $ on some other lenses that I wanted at that time. I even shot many pics at f/4.0 on many of my vacations and even family weddings, both handheld and on tripod. The 17-40 at its price, again is a winner.
Then, I purchased the 35L f/1.4 and the 24-70 f/2.8. Since the 24-70 is on my camera all the time. If I want high quality images, I will use my 35/1.4. If I want wide angle, I will use the 17-40. Ever since I bought the 24-70 and 35/1.4, I seldom use the 17-40 anymore.
Early this year, I finally made the leap and bought 5D3. With 5D3, the 24-70 again becomes my lens of choice, followed by the 35L. The 17-40 is only used when I want ultra wide. For all other photography such as vacation, walk around, street shooting, I would reach out for 24-70 and 35.
My point is, save the $ for other good lenses. When you build up your lens selections, you will notice the UWA (17-40 or 16-35) will be used less and less because it is just too wide. Also both 24-70 and 35 give better color and contrasts. So save some money buy the 17-40 and save the extra cash for something else that will give you more creative perspectives on your photography.
This is from my own personal experience. Hope this helps.