Bet that title scared most people.
Anyway, Peter Norvig is Google's director of search quality - and semantic web ontologies simply refers to how different words can have different meanings to different people on the web - and how Google's big challenge is to determine probable required meanings and deliver on those expectations.
There's a speech he gave on the issue, which can be found here:
Semantic Web Ontologies: What Works and What Doesn't
Interesting reading, though it's a shame they didn't include the graphical representions referred to in the presentation text.