I'm sure you all know about
Kindle Matchbook, and possibly also University Press of Kentucky's
e-book loyalty program.
I've just launched
Digital Reinforcements, which is basically the same thing (buy the paper book, get the ebook free). I've done it by putting a code in the back of the paper book, which can be used at the checkout on my website.
Has anyone here done anything similar? If so, how did it work out?