Ok I've had the lens back from Sigma. I did ask for my money back but as their warranty says - they don't warrant that the lens is fit for purpose so if you want a $400 paperweight get this lens!
It came back with an invoice saying that they had replaced the optics - well it's certainly different to what it was but it's actually worse. I won't bore you with images but it still has serious focus problems.
Any company that doesn't warrant it's goods as fit for purpose, in my view, should be given a very wide berth. Save up a bit longer and get a Canon lens - in fact even the £90 18-55 kit lens with the 20D is better than this one