Simple - the idea that the current state-of-the-art in search is what we'll all be using, essentially unchanged, in 5 or 10 years, is absurd to me.
The web is big. Really, really big. It's literally billions and billions of pages. It's Carl Sagan big. And it's doubling in size every year or two.
So the idea that what you can see in positions 1-3 above the fold on Google are the sum of what the web has to say about every possible query is crazy.
And yet they have 85%+ market share, and little effective competition. At the same time there is such a fabulous business in search. It's the highest monetization service on the web, by far. Why does this Coke have no Pepsi?
Having just spent 5 years in the media space, I've come away with the idea that editorial differentiation is possible. But the editorial voice of a search engine is in the index...so it has to be algorithmic editorial differentiation.
Google and it's copy-tition were designed 10 years ago. But the web has changed significantly in the past decade. Google was built to index a web that no longer exists... a web where people still engaged in social linking behavior, for one thing.
But at the end of the day, founding a startup has to be about personal motivation. My roots go back to os internals, networking, algorithms, and product boot-up strategies. Basically, trying to make algorithmic sense of the vastness of the web is a difficult but really interesting problem. So is tilting at the biggest brand on the web. It's all just plain fun, which ideally should be the point of working. ;)