Well I just posted over at Kobo's Facebook page and they said they are looking into it. Alot of people have not received their 50% off but one person just got theirs from yesterday over there after leaving a comment. So keep an eye out maybe they are fixing it.
Edit: The 50% off coupon just showed up in my email!
It does seem to be unlimited use and yes it's the same code that ATDrake mention.