Notes:
Mail:
Unsubscribe => send 2 mails, receive 2 mails; same for subscribe; so must send 4 mails just to resubscribe.
Better to subscribe from new address, then unsubscribe from old address, so that you don't miss any messages. But then you get duplicates.
Web:
Excellent for stuff like gnu.org. E.g.: changed my details for libtool@gnu.org, replied to a cookie for that and it updated all my GNU subs. But it didn't tell me about the other lists!