I have just noticed that if someone mails you and you have them on your ignore you still get the '1 Private Message' notification, when I click the link I'm taken to my inbox showing no unread message.
Can this be fixed? Id think that the best way to do it would be to prevent the user from emailing anyone who is ignoring them rather than allowing the mail to be sent and sitting hidden in the recipients inbox.
Alternatively allow users to set up rules that will auto delete messages from a specified sender.