While DH is a smart guy, one of our rules of thumb at YC is to be skeptical of any application containing the phrase "semantic web." It's a bad idea magnet the way AI was in the 1980s.
You're right, of course (and I need not point out the irony that DH was in deep with AI), but I'm holding out hope (and not just because I'm bitter that the Connection Machine failed!). The main reason (in my opinion) that the semantic web has failed so far is the reliance on 1) predefined, very limited ontologies, and 2) creator-generated rich metadata. Freebase seems to me like, if not the solution, at least a good step in the right direction in terms of addressing these. The real question, of course, will be whether a userbase springs up to keep it up to date, and whether the logic behind it can keep it reasonably self-consistent.
