Had one, didnt like it, prefer the results from the Sigma 17-70, and find the lens lighter too.
Another thing about lenses i dont like is the variable aperture through a zoom range, and both these lenses suffer the same problem.
I like my Sigma 24-70 f2.8 alot (Now that i got i back from Sigma, nice and sharp), and i want to invest in the Tamron 17-50 f2.8 if i dont upgrade my 40d to a FF or 1.3x crop camera. These lenses will serve someone better, and you can probably get both used for not much more then the 17-85is