http://www.lenstip.com …OS_HSM__Introduction.html
In summary they say
In the case of Canon the Sigma will have to compete with the EF-S 17–85 mm IS USM and the EF-S 15–85 mm IS USM models. The first device is currently cheaper than the Sigma but its performance and fastness are definitely worse. It won’t be a serious threat even though its focal lengths range is a bit wider. The focal lengths range and very good optics are the strong points of the new EF-S 15-85 mm for a change. From this aspect it is certainly better than the Sigma. The Sigma features significantly better light and lower price, though. It seems that both instruments will find a lot of enthusiasts.
