[abathur]

I'm really interested in semantic authoring (not really structuring data with semantics--but marking semantics within running text), though I guess I'm disinterested in the semantic web.

I agree with a lot of the problems noted in other posts, and would add two other problems from the authoring side:

1. Identifying and employing sound semantics requires a level of thought and clarity that I don't think most people are habituated to working at. It raises the bar somewhat on who can be contributing (either they have to understand and take care with the semantics, or you need a separate person to handle them?)

2. I may be missing some good tools, but I haven't been able to find a good low-friction semantic authoring experience. Even if you are mentally prepared to write with explicit semantics, it still adds a lot of friction to the writing process (or requires subsequent semantic-edit passes).