I have 8 credits waiting to be used (I can hoard up to 12) and I also didn't get the email.
I think it is aimed more toward people who actually use their credits up.
(It seems that being a member gets you lots of deals that make the books *better* than the credit cost and I end up paying cash for the sale items and saving my credits. My wishlist has a couple of dozen books on it, so it's not like I don't have any ideas for what to use them on, but it feels like a better deal to get them at $4.95 or $7.95 and use the credits for normal member-priced items later. I'm not waiting for books to go on sale; I just haven't had a chance to listen to any since I signed up, even though I had more than enough time *before* I commited.
I project that my time will free up over the summer and that I'll fly through my credits then.)