Very good 598 1

The sharpness is very good (except wide open where it default fishing), effective stabilization.

The focal ring is a bit hard, but nothing more.

The color rendering takes a little yellow.
Not kicking in RAW, I can fix all this with DPP, Comes with all Canon case (think Update).

Only flat, it is not recognized by DPP and therefore can not correct vignetting, distortion and chromatic aberration. But other programs seem to do it (for a fee).

Storage pouch of high quality, delivered with visor. The lens cover is a treat to put on or take, compared to canon, especially when known sun visor. And it takes much better.

I had to choose the 17-55 2.8 IS USM barrel, the price referred me to sigma, without regret.

Edit: I had the opportunity to buy lightroom 3 since. This stone is supported in all circumstances. Even fewer regrets, therefore.