Summary: This lens seems to be really solid. I like the zoom range. The extremely wide angle of 16mm is necessary at times, but like all wide angles you get distortion which is the nature of the beast. So I really like 20mm because it reduces some of that. 35mm is my personal favorite probably because of the shallower depth of field. Love the 2.8! I really don't have any complaints except the price.
Conclusion: Great value, the version II brought the price of the older version down. Was nice on the APS-C 1.6x crop 7D. Pretty sharp, shot mostly at f2.8 unless I was doing some architectural work. Fast, wide, creates some fun images.
Pros: Wide wide wide. Sharp. Fast.
Cons: Lots of distortion, good amount of vignetting.
Conclusion: This is one of my favourite lenses. Build quality is very good, along with IQ and versatility. I've recently sold this lens as I needed the funds for dedicated portrait lens due to my changing photographic style. It was such a hard decision, and do miss it for some of it's unique qualities. I will defiantly buy this or the mark 2 version again when funds allow! I used this lens on a full frame body, mainly for landscapes and photojournalist work.
Pros: Build quality, IQ, Focal length, sharpness, light but well built, great walk about lens.
Cons: Very soft around the edges at 2.8 on a full frame body!
Conclusion: This was my first Canon "L" series lens. I am using it now on a Canon 60D, with an APS-C sensor. So far, I am very pleased with the results. I can't wait to try it on a camera with a full frame sensor. It blows the other lenses I have out of the water, and this is now the lens I use most frequently. I love the sharpness and quickness of the autofocus. It is very good in low light, and the lack of IS is not missed.
Pros: Quick, accurate auto-focus, good contrast, good colour, nice bokeh.