No matter how many were affected, call your best 100 customers and talk to them about it. Say that you messed up, and are changing things to ensure this does n

No matter how many were affected, call your best 100 customers and talk to them about it. Say that you messed up, and are changing things to ensure this does not happen again, and then keep blabbing on until the phone call turns into a discussion of features and new stuff that your doing. Now you have a sales call. Every point of contact with a customer, even telling them you screwed them, is an opportunity for a sale, or at the very least to come out of the situation more understanding of each other.