It would be useful if a contact unsubscribe or opt-out created an activity. If it did, you could easily see a List of the contacts who have opted-out or unsubscribed sorted by most recent activity (i.e. the opt-out/unsubscribe date).
You can, of course, easily build an opt-out/unsubscribe list. You just can't see whether these are recent unsubscribes or ancient history. You have to dig through multiple screens on a contact by contact basis to see when they opted-out/unsubscribed.
