If you're logged into Amazon and visit the front page, you're presented with your Plog, or personalized blog. Basically, The Great and Powerful Amazon looks at what you've purchased, looked at, and rated and posts links to other items you might find interesting. It's the same recommendations they've always given people, only more timely (this DVD is out today, we thought you might like to know because you liked this other movie) and in easily digestable chunks. Blog as interface; the content exists and this is just another way of presenting it.
Update: Matt says that he's not seeing his Plog. Maybe they're only testing it for some people, so you may not see it when you hit Amazon's page.