The API to unsubscribe is
@subscriber = Subscriber.new("firstname.lastname@example.org")
I'd like to be able to unsubscribe the subscriber from any list they appear on, possibly by omitting the list_id argument to the unsubscribe method. Another way to solve this would be to provide an API to add address to the suppression list.
Thanks very much for the suggestions. I will definitely be adding both of these suggestions to our feature request list, and I can say with some certainty that at least one of these will be added in the not too distant future.
If anyone else out there would like to see either one of these features added to the API, throw your weight behind it here, because as with all new features we implement, it's the customer requests that determine their inclusion.