I got one as well a few days ago. It worked and everything. I don't know why I got it, other than I called Customer Services about trying to get my Fictionwise library transferred over, and then filled out a customer survey link I got in the mail. I mentioned how screwed up I thought they were making the whole FW thing by not letting their customers know in a timely manner what was going on and some realistic dates on the actual transfer.
The evening after my call all my books magically were transffered, and then the next week I get the gift card. So I'm not sure if one triggered the other or not.