(PS: After sleeping over pg's essay, I found it much less convincing the next day - implicitly, he's mixing up price with value, ignoring the temporal nature of markets and of opportunities - Google couldn't have been a startup in 1989 and Ford was a startup in the 1910s - and disregarding multi-product and B2B startups (premium Tibetan to Hungarian services) altogether. The clincher from yesterday - weekly growth of 7% - sounds like utter BS today.)
EDIT: Not sure why I'm being downvoted. I'm just pointing out that this article only and only defines a startup in terms of its worthiness to investors. It's as misleading as any other single-formula characterization of a complex multi-agent system. Startups != Growth, period.