Amazon's affiliate program has consistently been the worst performer by far over the past year or two. Their same-visit purchase cookie is super restrictive - I imagine this applies to MP3's as well.
That widget takes up a lot of space (and attention), cluttering any page it's on - just for the potential to earn 10 cents IF someone decided to whip out a credit card on the same visit? Or maybe I just don't spend enough time in the part of the web where these things will be popping up.











