If you don't tell it otherwise, the Amazon capsule will use ALL the words in the capsule title to search. If there is not a match for all the words, nothing will appear.
To keep the title and to better control what appears, use the right of the two buttons: "Choose keywords". Enter one or two words, and click "Preview Amazon results". This will show you what is going to appear.
For example, if you write a book review, enter the exact title in the keywords, and limit the capsule to just one result. Then, you have a picture of the book, and viewers can click and buy it.
(Also, I just checked on a hub of mine- the Amazon capsule is working fine, 10 am PST, 1-13-12)