It looks like a web page, but it's a full blown web app, tied to services all over the place.
Read on for an explanation of what's in the screenshot. John Battelle's article on Business 2.0 is also good reading. And of course, check out A9.
Update:the A9 diary is not a blog, it's for "[annotating] any page with notes", according to an insider.
The underlying search results are in part from Google, and in part from Amazon (the tagline at the bottom reads "Search results enhanced by Google. Results also provided by A9.com and Alexa").
The screenshot was taken with me logged in. You get access to things like a search history, showing recently visited sites, searches in the past 24 hours, and other time periods. Searches will also return results from your history, just as they will return results from any bookmarks you have.
The far right row of buttons controls what you see. Clicking the buttons displays additional columns, without any page reloading. The whole thing certainly does feel very interactive, and very slick. The application it most feels like is (perhaps not surprisingly) Google's Gmail.
The buttons control the display and search results from the following:
Amazon has always been good at turning searches directly into dollars, and they've pulled together some interesting partners. I'm of course especially curious about this mysterious diary component. And the big hype word du jour -- RSS -- is nowhere to be seen.