Yesterday I predicted that the Amazon Appstore would open sometime in the next week. I'm going to revise that estimate and tell you that I think it's going to launch today or tommorow. There's a high level redirect for the Appstore at Amazon.com/apps. The link is now live, but there are no apps in the store just yet. But, AndroidNews.de reported seeing apps on that page earlier.
I've seen this from Amazon before. The high level URL for the Kindle didn't go live until the morning of the press conference, so in this case I'm betting the AppStore will open today tomorrow.
P.S. I did try the other links on that page; they didn't work.