I'm a bit surprised, but naturally quite happy, that my little piece has generated so much discussion. Let me respond to a few criticisms.

• "This is just a rehash..." Yeah, the position I'm taking isn't novel. If it were, Shapiro and Rotenberg couldn't have already attacked it, giving me someone to argue against.
• "Disinformation"- OK, some people will lie on forms. If it becomes economically worthwhile to do so, firms will develop more robust verification schemes like Adult Check or rely on digital signatures publicly linked to verifiable identities. Or maybe they'll just be willing to accept a certain amount of information pollution.
• "You can't have a market for a 'negative good;' it's like paying extortion money, and generates perverse incentives." Privacy markets aren't really analgous to the case of the thug asking for a payoff to refrain from breaking your windows. Unlike the victim in that case, users ultimately control what information they want to release to websites. Someone's bound to mention cookies-- I'll just point out that those can be shut off, and more importantly, that future versions of the popular browsers are supposedly incorporating more robust cookie-screening features. Isn't it generally better on face to let a problem be tackled by this kind of individualizable, technological solution than by top-down control?
• "But you still need government to enforce contracts." Sure. I'm not an anarchist-- if a company lies about their practices in a privacy policy, that's fraud. Same as when any other business lies about their product or practices. You should be able to take them to court.
• "Who would bother to do all this haggling?" or (in economese)"This raises transaction costs- Inefficient!" I tried to deal with this objection in the article, but let me add the following to what I said there. There exists a strong incentive for either 3rd parties or software protocols to be developed, which make it easy for users to deal with privacy issues. Maybe you set your browser to block any page demanding more than a certain amount of information. Or maybe you allow it to offer you various prices on a case by case basis, or to auto-accept offers of (say) a certain discount level for different kinds of information shared. I flubbed in the article by attributing similar features to P3P, when apparently they've been removed since I wrote the piece some months ago. I'd still say it's a safe bet that something along those lines will emerge.
• "But you can't sell yourself into slavery, why should you be able to sell your privacy?" This is just a bizarre analogy-- there are very specific reasons why slavery contracts are morally suspect, and they don't cross apply to privacy in the least. If I want to publish all my private information on my webpage, I have a free-speech right to do so, don't I? If privacy were truly inalienable, I could legitimately be prevented from doing this by law. If we then decide privacy is *not* inalienable, the addition of an economic incentive to speak can't possibly make it so.
• "If most people don't care about privacy, it'll be harder to find sites that respect it." I think this is also addressed in the article. There's no inherent right to shop on the web on your most preferred terms. And I certainly deny that we have a right to make everyone pay the costs of the privacy we demand.
• "This is wacky free-market utopianism with its head stuck in an econ textbook." Actually, I thought of the article's primary argument as moral, not economic. But as for the economics-- what in particular is wrong with the argument I lay out? This "perfect markets fantasy" thing is a strawman-- nobody believes in that, least of all me. The question is whether markets tend to approach an efficient outcome better than do regulatory schemes. I don't need to claim that markets will make all the children of the world sing together in harmony, just that they'll perform certain tasks more effectively than the alternatives.
• "You're a silly libertarian who argues at an 8th grade level and can't write." Guilty as charged.