I realized today that a great deal of what gets sent to the "Bulk Mail" (SPAM) folder in my Yahoo account is actually stuff that I've either explicitly or implicitly asked to receive over the past several years. Tired of seeing it pop up in my Inbox, I've just told Yahoo to treat it as spam and get it out of my face. I just have far too many unwanted "subscriptions"; opening each e-mail and following the instructions for unsubscribing would take more time than I'm willing to invest.
This leads me to an interesting idea: why not make an Internet subscription much like a subscription for any sort of printed thing that you ask to receive by regular mail? Why not define subscription periods (weeks, months, years, whatever) and require an action by the user for subscription renewal? If you're looking at the e-mails regularly, you won't have to worry about your subscription expiring, because you'll get a reminder in a prominent place within the e-mail's body. And if you are routing the e-mail to your spam folder, it will eventually stop coming.
As I see it, everyone wins. The company sending the e-mails is not left with a bloated mailing list that inaccurately represents how many folks are actually still interested in the mailing. The user never has to go out of his or her way to remove something that is already a time-stealer for him or her. The provider of the e-mail service would use less bandwidth because it would be transferring less e-mail. Sounds pretty good to me.