I have submitted my apps to Amazon Store. One of them is on top of rankings in its category. Still it is just a little percent of downloads comparing to Android Market.
I know of almost a dozen Kindle Fires that parents are holding onto to give to their kids at Christmas. I think the Amazon downloads will pick up quite a bit in the next 3 months, especially for apps that could appeal to older kids. But it'll be interesting to see how the Amazon numbers compare to the Android Market.