Excerpt: Use it with C-100, 7D and 5D, along with 24-105 L and 70-200 L. Love it. Biting my elbows for not buying it long time ago. Gives me perfect range to do wide that covers almost any room, and go in for a waist up shot if needed, as well as just sufficient for establishing shots / exterior shots. Almost a default lens. Great L quality, that's a given.
Pros: Consistent Output, Durable, Rugged, Strong Construction
Excerpt: I use this lens for weddings and production shoots on a 5D mark iii. The resolution is outstanding. It's just wide enough to make walking motions very smooth, but not as wide to make everything look "bent." You don't necessarily get the manipulation as you would with an 8mm or so, which I prefer. This lens is also easy to focus with manual focus, which I also like using since I'm moving around a lot, or at least my subjects are.
Pros: Durable, Fast / accurate auto-focus, Good in low light
Excerpt: This is a lens I've wanted for some time. This will be used for a wide variety of things. I'm beginning to get into high-end real estate photography, and this lens is perfect. It's also great for landscapes (I think that's a given) and, as I've come to discover, maritime photography. Just like real estate, the wide angle lends itself well to shooting boat interiors. I can't imagine being happier with a lens than I am with this one...
Pros: Consistent Output, Durable, Easily Interchangeable, Fast / accurate auto-focus, Lightweight, Nice Bokeh, Rugged, Strong Construction
Excerpt: Love this lens. I needed a higher quality wide angle lens that the kit EF-S lens that came with my Crop camera as I knew I was going to go FF eventually. The kit was slow to focus and the images were just not that sharp. Once I put the 17-40 L on my cam body I knew I had the right lens. It has great image quality and focuses extremely quickly. The L build quality has stood up to one accidental drop with absolutely no issues aftwards.