Usually when I read stories about mysterious search engines I always think that this is a good PR for anyone with a new product in the search market.
Powerset actually firmly believes that they are "fundamentally changing" the web search with their new natural language search. What Powerset is actually doing is paying attention to common words like “by”, “for”, “of”, and “in”, that all the other search engines like Google are ignoring.
Considering the fact that there are billions of pages with millions of "stop words( “by”, “for”, “of”) I think it will be very hard for a search engine to solve the problem and come up with a successful algorithm. But may be I am wrong. For more details read TechCrunch post.