Killer applications solve real problems. What is the biggest real problem on the web today? The noise flood. Can semantic web standards help with that? Maybe! Something about trust, integrity, and lineage, perhaps.
Semantic Web doesn't help with the most basic thing: how do you get information ? If I want to know when was the Matrix shot, where do I go ? Today we have for-profit centralized point to get all information, because it's the only way this can be sustainable. Semantic Web might make it more feasible, by instead having lots of small interconnected agents that trust each other, much like... a Web of Trust. Except we know where the last experiment went (nowhere).