Picked this lens up at a 10% discount from Abes of Maine. Very impressed. Great build quality, and well designed lens. HSM is very silent, but this variant of HSM does not do FTM override. Has focus lock, but have not experenced any focus creep even without using it. Very stable build. Focus barrel is one piece and built to very high tolerences.
Very sharp even wide open at all focal lengths. Focus is very accurate, and spot on again at all apertures and all focus lengths.
Contrast focus works very well with this lens also. Slower than phase, but works very well and again very accurate.
Compared to the Canon 17-55 the build quality of the sigma is much better. Built to much higher tolerences and zero zoom creep. I feel as though the sigma is noticably sharper in the center and mild edges than the canon, but the canon as the edge focus at 2.8-4. At F/4 the two are neck and neck with the canon taking the far edges while the sigma is sharper in the center and mild edge. Colors are a touch warmer on the sigma than the canon, and flare is MUCH better on the sigma than the canon.
HIGHLY Recommended, especially at this price! cant beat it!