I have found that disabled and hidden users (Hidden by superior or directly) continue to receive notification emails. The only way to prevent these emails is to either delete the user or login as that user and delete their notifications which is not possible for a user to do if they are hidden or disabled.

We have found there are situations where disabling a user or hiding entire groups of users is required, but their notifications need to also be stopped.

Note: Checking each users account prior to emailing may also open the door to include new enhancements like this: http://issues.ez.no/IssueView.php?Id=13649