Reprise: Emergent structure vs. intelligent design
This all reflects a fundamental if still incoherent debate. There's one school of thought that says that if you just collect enough data and throw enough algorithms at it, the inherent structure - and the understanding of that structure - will emerge. After all, that's what happens with human beings, though it takes a decade or more. (And in some people, the process even continues into old age.) The recent explosion of tagging is taken as evidence of this: With their tags, users are creating implicit relationships among online objects, and indeed, complex webs of relationships are emerging, with nodes, clusters and other rich structures. But the relationships themselves are poorly defined, other than strong or weak - and possibly, links made by my friends or by trusted authorities, vs. links created by anyone.
By contrast, the opposing point of view says we have to hand-design the relationships and structures - like the complex database schema about cars.
Where Metaweb differs from that approach - and from "ontology" projects such as Cyc - is this: Metaweb's creators have "intelligently designed" the grammar of how the relationships are specified, but they are relying on the wisdom (or the specific knowledge) and the efforts of the crowd to create the actual content - not just specific data, but specific kinds of relationships between specific things.
Metaweb has a process (including editing and approval) for people both to define relationships, and to use those relationships to describe specific instances.
At least for now, the Metaweb approach is more likely to yield short-term results that look intelligent.