That this comes out from Bray's point of view as less intrusive than cookies is beyond me. I use Spamhole religiously when asked for an email address. The important step here is that the friction of the signup will make the URL for the RSS feed (or other HTTP headers as suggested) precious to you, so that you will keep using the very same one. And if friction is high enough you will even make sure to transfer the URL to other machines as required.
I've been intrigued for a long time about the notion of precious URLs. Good permalinks are precious. Google cache links to vanished pages are precious.
I think precious URLs would form a great way to introduce micro-economy to online publishing.
The easy way to think about them is Bray's way: If advertising is supposed to matter to the RSS publishers, then subscriber counts must be measurable and precious URLs is the way to go there.
But one can easily imagine a client side version of precious URLs also. It would rely on a new enriched client. When loading up a website the client would negotiate in the background the licensing terms for the site through site metadata. After negotiating terms the site would then publish to your personalized precious URL's - e.g. by proxying the precious content through the licensing client. The licensing client would implement strict observance of URL expiration time, ensuring that your money is not wasted by continued reloading. Client side, you may stipulate how much money you're willing to spend in a given amount of time, how much without being asked, and how much at a specific site.
While the interaction is designed to provide transactional security, the individual load occurs in the background and is not viewed as an economic transaction. The model is 'metered surfing' You're simply charged a bulk amount per month, and conversely the website does not enter into a transaction with you, but is reimbursed for number of served pages.
It's just another micropayment scheme - but I think the importance of introducing a kind of friction sufficiently harmless that we can accept it happening in the background is important.
The New York Times costs approx 1$. One would expect to surf the website for some fraction of that per day, which means that a particular page should cost no more than a penny or two.
I don't know of anyone using micropayments as minute as that on a regular basis, but mayby iTunes will change that. If permanent ownership of a song is only 1$ surely you would expect to be able to buy other media for that kind of money also.
While we're touching on the subject of giving out emailadresses: I couldn't be bothered to keep giving out the same address. Sometimes the disinformation of changing address is even intentional.
Ironically Spamhole has changed their website so that the friction of creating a spamhole has gone up a lot. You now have to sit around and wait for confirmation emails with confusing validation instructions. That is not just bad. It is unusable.