I bought this lens about 6 months ago, and I've really never used it. I have a 16-35 F/4, and I've always used it for the 35mm length. Last week I spent a few hours looking at "sharpness" ratings on DXOmark and MTF charts between the 16-35 F/4 and the 35 F/2 IS. I was quite impressed at how much better the 35 F/2 is at F/8. I shoot primarily landscape, so I'm usually at F/8 to F/11.
Because of my new found knowledge, I'm going to shoot a lot more landscape on my 35 F/2. From my few hours of MTF comparisons, it may be the best MTF performer, EF mount, at F/8 than any other lens I looked at, including Sigma, Tamron, and Zeiss.