Excellent post on structure vs. data, the soundbite is
Data First strategies have higher usability efficiency (all rest being equal) than Structure First strategies.- which means nothing but the following: Structure is unnatural for us, it must be learned and until we learn we are challenged by structure. Data, more naturally, is just language and we've been wired for that for 40000 years.
On the other hand as the post notes, structure works. If you can hide the structure and use it then structure is very efficient.
The only problem wth the last assertion, and we're learning that during the current "remix everything" paradigm and the emergence of the hypercomplex society, is that we quite simply can't keep up - and that the structural efficiencies that we're used to are too expensive to be valuable when the structure we apply them to are as volatile as structure is in our highly mutable digital society.
This is also the reason why microformats have been so hugely successful and why the semantic web, old style, is unlikely to succeed in the near future.