One feature that is sorely missing is the ability to create dynamic domain distribution lists from the GAL. Say I want to create distribution lists for various departments that I communicate with frequently. My current choices are to either create an alias or a mailing list. Both have significant limitations in that they are static lists; If the email account is disabled or deleted, the change isn't reflected in either list.
A dynamic distribution list created from the GAL would automatically be updated when an account was disabled or deleted. Ideally, these distribution lists could be exposed in the GAL so global distribution lists could be created allowing anyone within the organization to send an email to "Sales", "Support", "HR", etc.