A "new" Plan for Spam?

This article on a new plan for spam makes for an interesting read. The author asserts that Bayesian filters are becoming less and less effective, and that a radically simplified challenge-response system is the key to really killing off spam.

Personally I'm finding that Popfile (a Bayesian filter) combined with an anti-virus checker works very well. However, I accept that some of the anti-Bayesian devices he describes may become more common in the future. His simple challenge-response approach essentially revolves around asking the unknown sender (for it is only unknown senders that are an issue) to send a second mail. I think it has a lot of merit, with one important caveat that he doesn't mention - you will still need a virus checker, as many e-mail viruses rely on sending mails from trusted/known individuals.