I just bought this lens today and after a full day of testing the lens I must say I'm impressed. Since I've been pondering the idea of investing in a lens I couldn't really decide between the EF-S 10-22mm and the 17-40mm. I liked the UWA of the 10-22 but wasn't sure if I would use the lens on a daily basis. I'm a big fan of prime lens but I also must say that carrying 3 lens and + in your bag and swapping them all the time to get different shots is a bit annoying.
The 17-40mm delivers a good IQ, sharp, colorful and consistent. On the down side I found that it tend to overexpose the sky in some situation but eh, it's only been one day so I guess I'll get better with it (plus NYC is quite smoggy lately). I've read quite a lot of good and bad reviews on the lens, some saying the IQ at the corner was inacceptable at f4. I must have a good copy since mine gets very little distortion at f4-6 and none over 6, but that's a different story for FF owner which isn't my case. Overall good performance and looks solid.
If you're looking for a good lens and don't wanna break the bank for the 16-35mm this is a good alternative (not as good but...). I do recommend a filter for it (UV or clear, up to you) and if you can afford it get the prime 50mm f1.4 so you're covered for portraits and those low-light shots.