Re: the new $5 credit promo
I received the same e-mail. The credit is applied on my account, added to my store credit balance. Fine print says (emphasis mine):
The $5 addition to your account is a limited time offer and may only be redeemed for eBooks and magazines. The total amount of $5 will be removed from the customer's account if not used partially, or in full by 11:59 PM EST, on June 15, 2015. This offer is only available in Canada and the US.
What pressure to find something to use it on!

I'm assuming I just need to put a dent on it and the remaining credit is mine…although with Kobo, we really never know.