I shoot weddings and other large social events, as well as child and family portraiture. This zoom range and the constant f2.8 aperture serve me well in this kind of shooting.
This is a superb lens, the sharpest ultra-wide angle zoom I've ever used. I use it almost exclusively at f2.8 when photographing people at events and I have no problems with the significant light fall-off off-center. There are very cool looking 18 point stars when it's used at around f11, which gives rooms shots a little extra punch if you plan them accordingly.
You don't use this lens for its out of focus blur, but I love getting close to subjects and have found the bokeh rendering to be a very pleasant surprise when I do.
It's an expensive piece of glass, but for me it will pay for itself over time and meanwhile it's a business write-off. The significant cost of this lens will probably dissuade many people from buying it, but whoever takes the plunge will be rewarded with beautiful rendering and rock-solid performance.
I actually owned Canon f4 version of this zoom lens. That one comes with IS and is also truly excellent. I lost that lens in an accident and would have been happy to buy another if the f2.8 version hadn't been upgraded to this beauty.
For anyone shooting mostly landscapes, the f4 version is amazing, probably indistinguishable from the f2.8 version when both are stopped down between f5.6 and f11. And the f4 version is much lighter, too. Users of Canon's 24-70 f2.8mk2 will be surprised to discover that this lens is actually longer and heavier than that one. No complaints here, it's built like a tank and I love it.
You can't go wrong. It's a great time to be in the market for wide angle lenses from Canon. I covet the remarkable 11-24, but wouldn't dare use that lens at events because it can't be protected.
I heartily recommend this lens. And Best Buy's protection plan is actually one of the real-world best I've ever experienced. Wouldn't buy any equipment like this from them without the Geek Squad protection. What I wasn't thrilled about was (1) Best Buy doesn't have this lens in stock in any of its stores and (2) the lens was shipped in a bubble wrap bag with no protection other than Canon's packaging. I was lucky, the lens arrived intact and has been a stellar performer. But Best Buy should put this lens in a hard cardboard box and surround it with cushioning.