CCBill only offers an option to auto-create both random usernames and passes. And when they say random, they mean it.
Lower/uppercase letters and numbers mixed. That much more security than necessary, and it causes a shitload of login probs for members.
You can generate you own user/pass lists with some tool though and upload them to CCBill, that's what I do. Simple lowercase letters only usernames, and lowercase letters+numbers passes. Works like a charm. Totally crack safe, and no support trouble with members.