Nvidia cards are catching up though. Might go and check out the cuda development thread for more information.
Dollar-for-dollar, the AMD cards still offer a more than 2:1 advantage over NVIDIA despite the increased gains via cudaMiner. Thus why I only suggest using them if you already happen to have them and not go out to buy one specifically for mining. That said, though, cudaMiner gives me hope that perhaps that performance gap can close more.