Amazon Settlement Credit
If you bought Kindle books between April 1, 2010 and May 21, 2012 check your email for an Amazon email as to a possible settlement credit in relationship to the antitrust lawsuit with the book publishers. Amazon was not a party and is just distributing the settlement credit from the book publishers.
The amount varies based upon your purchases. In our case the credit is $331.23 so is a significant amount of money. The credit can be used only to buy books (Kindle or regular) and is good until the end of March, 2015.
Our credit is so high because it was during that period of time that we replaced every book we owned that had a Kindle edition.
Anyway, wanted to point this out as some might think that this was not legit, but it is legit.