What are the ramifications of a customer's Payment ID being leaked (in regards to past orders, assuming it is changed once the leak is discovered)
As mentioned above, I think the payment ID being leaked could only indicate that someone made a payment for that specific amount at that specific time. Assuming the info is leaked with identifying information, then yes, you'll know that Jane paid a particular amount at a given time. You wouldn't be able to do anything more with this info, unless Jane continues using the same payment ID.
Does mixin count increase the time required for confirmations? Does a transaction with a higher mixin count have to "sit and wait" for additional transactions to occur on the blockchain, in order to mix with them? What if in a given minute or period of minutes, there are no additional transactions, only the "mined block reward(s)?" Can a high mixin count transaction mix with block rewards?
Let us discuss...
As far as I understand cryptonote (and also bitcoin), the mixin count does not increase the time required for confirmations - the ring signature stuff is passive - its just pulling information out of the blockchain at the instant the transaction is created. It doesn't have to go anywhere to get ring signed.
and what effect does mixin count have on the anonymity of a Customer whose Payment ID is publicly known?
Hrm, I think it wouldn't do much do to the stealth addresses.