I've only added 2 books to my library since using up the last of my mountain of no-rush credits a few weeks ago. Both of these books were free (1 from Kindle First and 1 from Samsung free book thingy)
However there's a £12 Amazon credit coming my way. They've just recalled some UK power adapters that were bundled with the Fire 7" - options are either get a free replacement adapter or a £12 credit to you account
I've never even used the bundled adapter so...