Here at ParseHub, we're attacking the problem from another angle. Our tool lets users turn semistructured html (even the complicated, interactive kind) into structured data. The user does this by visually describing relationships in and across pages.
The key idea is to make it easy for another party to add the semantics on top of your data. This solves some fundamental issues that you and Cory Doctorow mentioned:
1) The economics equation for tagging now works out. The user that's doing the tagging has an immediate need (and payoff) for doing that tagging.
A corollary of this is that the parts of the web that are most valuable (in the sense that users need them the most) tend to get tagged first.
The following are responses to Cory's essay:
2.1) The person that's doing the tagging is also an end user, so there's an incentive to do the tagging honestly. That doesn't stop the underlying website from lying. But that's an issue with the web in general, and is mitigated by things like SEO penalties, reviews, etc.
2.2) Again, the tagger is the person who benefits from the tagging, so as long as the data is valuable enough, it will be tagged despite laze.
2.3) We haven't overcome human stupidity. Presumably since the person tagging the data needs it, it will be at a "good enough" level to be usable.
2.4) This one doesn't apply; the tagger is a different person.
2.5) 2.6) and 2.7) These are tougher, and we haven't started working on them yet. You have the same problems when trying to consolidate data from multiple sources. One possibility is to have several alternatives and allow searching to choose between them. That's how Bloomberg solves some of these problems, though it does result in fragmentation.
I'd love to talk to you about this some more. You can email me at serge@parsehub.com
Full disclosure: I'm one of the founders of http://www.parsehub.com