Remember that Radiohead experiment back in 2007, the one where they allowed free downloads of their latest album and asked listeners to pay what they felt was fair? Some say it was successful and others beg to disagree. Assuming Amazon...
I think that the debates over owning vs. subscribing, pricing vs. donating, supporting vs. freeloading are some of the most interesting aspects of the move to digital distribution.
Would this work for Amazon? I think it was generally considered a success for Radiohead. I know I "bought" a copy.