WARNING!
Here's what I found hiding deep in the Amazon.com website after I've been charged again on the songs I already purchased due to the fact that the downloader failed and I had to download them again:
A:
Your Amazon MP3 Music purchases can only be downloaded once. After you have successfully downloaded the file to your computer at the time of purchase, we recommend that you create a backup copy.
We are currently unable to replace any purchased files that you delete or lose due to a system or disk error. If you encounter a problem with an MP3 file immediately after purchase, please click the Customer Service button in the Contact Us box in the right-hand column of this page so we can determine how to help you.
So, unlike eMusic where as you can re-download the songs you purchased, Amazon.com will actually charge you to the same payment card without needing your input of the info...beware of this. If you ever encounter a problem with a paid MP3 from Amazon.com, remember to contact its customer service first.
However, the good thing is this is America, you can always write to request a refund if a proper reason stands.