YET ANOTHER SOLUTION TO SPAM
"Imagine a system that lets you set up a kind of electronic guard dog that would police incoming e-mail. Using a set of user-defined rules, e-mail from preprogrammed domain names, such as yourcompany.com, would be sniffed and automatically approved. So would messages from friends, family, prior correspondents and known mailing lists.

"Unknown correspondents, on the other hand, could contact you only if they paid for the privilege. Without bothering you, your guard dog would reply and tell the sender how much "postage" he owed. It's likely that a polite custom would arise: If the message you received from an unknown sender was sufficiently interesting, you'd return the payment or simply not deposit it.

"...Then again, the postage would not have to be paid in legal tender. Any activity that cost the sender enough would do the trick. One scheme that's been proposed uses computation instead of currency. Called 'HashCash,' it requires the sender not to send money, but to instruct his computer to perform an arbitrarily complex calculation that would take a few seconds even on a fast microprocessor. Think of it: If a would-be spammer had to perform even three seconds of computation for each person she spammed, the pace of spam would slow to glacial."

Link to Declan McCullagh column

Sounds complicated. Perhaps we could just all agree to never do business with spammers and they'd all stop because it wasn't worth their efforts. I suppose, though, that someone will always waffle. Maybe we could figure out a way to shame people for responding to spam. We could get all of the email reading programs to include a pop-up that would say nasty things to people who open possible spam messages. "This looks like it might be spam! Conscientious people don't read spam. And they certainly don't buy from spammers. Be real friend. Hit the delete button!"