Right now an unconfirmed account is counted towards the payment quota.
The big problem is: Once a user enters as "unconfirmed" and does not confirm via the ONLY email he gets, he will stay unconfirmed forever.
What's worse: Apparently he cannot even resubscribe (it says "Subscription Error: This subscriber already exists") - so, the user has no chance to ever get his account confirmed, if he misses that single confirmation mail.
I'd love to see some changes in handling unconfirmed accounts, e.g.
1. Allow us to automatically resend the confirmation mail 2-3 times (e.g. after 12 hours and 24 hours)
2. Add an option to "Delete unconfirmed accounts after x days"
3. When an unconfirmed account tries to re-subscribe, please start the confirmation queue again instead of telling the user that his account already exists