Are accounts that mark an e-mail as spam auto-unsubscribed from the list?
I notice aweber do this - what about CM?
It seems a large percentage are hotmail addresses - I've heard that many users use the spam button in preference to delete.
Email addresses marked as spam are indeed automatically unsubscribed and suppressed from future contact.
It is true that for some Hotmail users they'll use the report as spam button as a way of deleting or unsubscribing, for others though they do feel it's junk, you never really know.