Sure. A lot of stuff is structured and some standardization may happen there. But let's say that somebody posts a really good comment here that becomes an aut

Sure. A lot of stuff is structured and some standardization may happen there. But let's say that somebody posts a really good comment here that becomes an authoritative source on something or another. You're not going to get the sort of fine-grained meta data that the semantic web expects. Titles are boring. We can get that from HTML already. And web search got a lot better when that and a lot of other structural metadata started being almost wholesale ignored. Where I could see the semantic web catching on would be in things like Amazon shops or something, where it was advantageous to be able to provide a homogenous interface to a given set of structured data. On the other hand, it wouldn't be in Amazon's interest for that to be the case, because for them the world works better when they get to define the rules and the API and it doesn't easily transfer to another store.