See
Sigma 17-70mm f/2.8-4 DC Macro OS HSM (Tested)
In my quest for a stabilized, large aperture, standard zoom lens that doesn't require a second mortgage, I had high hopes for this one. The Tamron 17-50/2.8 disappointed, and while this one is better, albeit slightly slower, I'll wait for a review of the
Sigma 18-50mm F2.8-4.5 DC OS HSM before I admit defeat and go back to a stabilized body.
It's got a lot going for it. It's better and faster than the kit lens, but so is the unstabilized
Sigma 17-70mm f/2.8-4.5 DC Macro.
I just miss my Tamron 17-50/2.8 on my KM5D.