If you could build a better search engine than Google what would happen to Google?
GOOG can monetize search better than anybody else. That's what the recent YHOO/GOOG deal is about.
Google has the best monetization platform for search not because it has the technology, it's because it has the infrastructure: people and offices. It's about sales and relationships not about ad servers. That's what MSFT needs to realize.
And that's what makes Google tremendously difficult to challenge.