Here's a sample Product Cloud widget, and a short description from Amazon:

"The Product Cloud widget shows clusters of product titles that are relevant to your page. The font size of the title in the cloud indicates how relevant the product is to your page - the larger the title, the more closely the product should match the topics on your page. This widget is ideal for sites with changing content such as blog pages. It will keep up with your changing page by automatically showing new titles as your page evolves."

I did notice that it took a few minutes for Amazon to figure out what this page was about, and the first few times I viewed this page, the Widget displayed a random collection of bestsellers.