I agree with most of the comments here - whats the point? this is Canon's kit lens for many of their deals and it's pretty good. Even if the Sigma is slightly better, I don't think people will fork out $ for something that many people have or know someone that has.
I think they need to offer something either different or better and this looks like none of those things.
+1 ... I think this new Sigma lens will most likely eat into Nikon and Sony sales than Canon (coz Nikon equivalent is too expensive and Sony does not have a similar lens).
BTW, I checked out your website ... great portraits, very beautifully put together.