Still too little too late. There is a lot of buzz on the net about how these cards are an epic fail for Nvidia already. Kind of hard to say that when they arent even out in the hands of consumers yet for real. MaximumPC got an engineer sample for their newest issue and pretty much got a boner over its performance (they are nvidia fanboys to a t, though they are even keeled with ATIs stuff).
Performance doesnt mean jack if people arent buying your products.
Another thing, the 4870 wont win performance crowns, but its either neck in neck with both GT cards, a little behind, or a tad bit ahead in some tests. Thats enough to garner it alot of market share. Same goes for the 4850. I cant wait for price cuts on these cards.