I agree that the focus ring is a bother...but I can live with it comparing the $500 diff for the OEM 17-55. I've also did a random test against my ef-s18-55, I do find that Sigma have the purple fringing while the kit lens don't (this is when i go into 100% to be able to see the fringing clearly..).
I really liked the feel of the barrel and build of the sigma. The zoom ring also has a unlock to prevent the lens from creeping. Other than the green/purple fringing and AF ring, its really really good. But it could be a deal breaker for some, such as myself. For cash, it goes for under 800+ for a grey set which cost half the price of the Nikon 17-55mm, but hey. You pay for quality in the end and the Nikon with it's ED element = superior pics at 2.8 for all lengths, all the time. Who knows, maybe by the end of the month, we would have a revision of this lens or some useful DX lens.