I've got a new Kobo and, although I've heard it used to show book covers when sleeping, mine only shows the FNAC logo in the screen. First I thought it used to happen because I was only using it to read Pocket articles, but then I started a book and it's behaving the same way.
It turns out it's a factory setting for the FNAC versions. It can be changed by connecting it to your computer and editing a file inside a hidden folder:
You should change it from
This was found at a MobileRead Forum post, and I thought it should be here for making it easier to be found.