A couple of trenchant quotes:
The social tagging systems are a laboratory in which techniques of statistical classification will be explored. As Clay Shirky has pointed out, the terms “movies,” “film,” and “cinema” are not just synonyms; they encode real cultural differences. A taxonomy that stamps out those differences won’t serve the various constituencies. We can still build systems around taxonomies, but we have to let the footpaths emerge, and in this realm they’re just fuzzy statistical traces.
Describe your domain of discourse as well as you can, because shared context makes communication more efficient. But don’t assume that your schemas are completely accurate or that they define the entire domain of discourse. Systems must be “dynamic enough to extend and refine their context through experience — i.e., they must learn”.
Good advice for a loosely-coupled world, though following it is easier said than done.