8 out of 10 points and recommendedLighter, Less Expensive than the Nikon option. Generally very good overall sharpness and excellent in the center. StabilizationCorner softness at f/4 or less when wide.
I wanted a fast normal zoom to use with my D300. Based on the many reviews online it was easy to narrow my decision down to two choices, the Nikon 17-55 f/2.8 or the Sigma 17-50mm f/2.8. I decided to get the Sigma since it was half the price of the Nikon and had VR. I have never used anything but Nikon glass for my Nikon cameras so this was outside the box for me. I was concerned about build quality and image quality, sharpness in particular.reviewed December 7th, 2012 (purchased for $609)
The first lens I received had an obvious alignment problem, the left side of the frame would be very soft while the right would be sharp even at f/8 on equidistant objects. I exchanged the lens for another sample.
When I got the new lens I shot test images using a D300 to compare the Sigma 17-50mm f/2.8 OS HSM lens to Nikon's 18-70mm f/3.5-4.5 AF-s and 18-200mm f/3.5-5.6 AF-S VR. I was specifically interested in determining whether to keep the Sigma or return it and get the Nikon 17-55mm f/2.8 for TWICE the price. After seeing the results I decided to keep the Sigma. It's faster and sharper than what I was using, it's half the cost of the equivalent Nikon option, plus I get VR. Central sharpness on the Sigma is excellent. Corners are soft at the wider settings below f/5.6 but as focal length increases past 35mm the image sharpens up nicely even wide open everywhere but the most extreme borders.
Link to images: <a href="http://www.lamarlamb.com/Things/Testing-Sigma-17-50mm-f28-OS/26935388_MqHphg#!i=2257949078&k=QzNjTXT" target="_blank">www.lamarlamb.com/Things/Testing-Sigma-17-50mm-f28-OS/26935388_MqHphg#!i=2257949078&k=QzNjTXT</a>