So, it's under warranty, why not just get them to fix it?
I had my 20D replaced by the dealer becaue it wasn't focussing accurately enough on racing cars. Now I admit I was pushing hte camera to its limits, but the second body works fine.
A good dealer can really save you a lot of pain here, rather then going for the cheapest supplier.
I used a Canon Pro dealer.
When they saw the results withe body I brought in, we tested the new body on passing cars and pedestrians before I left
Since then I've got a 1DSmkII refurbished form the Canon on line shop on ebay, works great and nearly 25% under shop price.
I wouldn't abandon them without giving them a chance to fix it.