I never understood why people use the same exact email address to sign up for multiple sites. Any decent MTA will give you a wildcard extension on your username, so signing up for service Foo means telling them something like [email protected]. An unsubscribe is as simple as forwarding that specific address to bounce, /dev/null, or their whois contact information (although I generally reserve that last one for articles that pop up a subscribe box when viewing). This also gives you the advantage of seeing who has sold your email address.