I signed up ages ago, and get them regularly. There are a number of different e-mail things with coupons.
They come out at different intervals. I heard someone say to give it 6 weeks. Apparently some are only sent out periodically and some are sent out weekly or more often (I'm sure I get them at least weekly).
So check what you're signing up for to make sure it's what you want--and check your spam box.