From the Omakase Links FAQ:
With Omakase Links, Associates can now automatically display the products and content that visitors to the page are most likely to buy.Unlike Google AdSense, Amazon Omakase appears to be personalized. Not only are the ads picked based on the content of the site, but also based on each individual visitor's interests; different visitors may see different ads depending on their interests and needs.
Adding Omakase Links to your pages is easy. Use the Build Links tool to select the appearance and behavior of the ad, and then simply cut-and-paste the code into your template or Web page.
Your page will now display Omakase Links and after a short learning period, the ads will be optimized based on what the Associate has been successful with in the past; what that user has been interested in; and what the site is about.
Because Omakase Links optimize on more than just the page itself, Associates may see a range of different products in their links but they will also see that the links learn what their visitors want.
In fact, because Omakase Links aim to show the right product to the right person, each person visiting their site may see different products.
See also my Feb 2006 post, "Amazon version of AdSense?", where I said "Amazon.com, with their expertise in personalization, is well positioned" to create "a future of personalized advertising" where ads are "helpful and relevant".
[Amazon Omakase found via E-media Tidbits]
Update: The first three links in this post (to Amazon Omakase, Amazon Associates, and the Omakase FAQ) require login. Not sure if a normal Amazon account works, but an Amazon Associates account does.
Update: I just saw an example of Omakase in action on a weblog. The Amazon ads were for products strongly related to my recent browsing and purchase history at Amazon, but unrelated to the content of the blog. All five of the ads struck me as relevant and I clicked through on two of the five to find out more about the products. Very interesting.