I read a fantastic post by Paul Graham tonight, Startup = Growth in which he systematically ripped apart my thoughts on startups. If there is someone who can define what startups are about, it is Paul Graham.
I have misjudged many companies as startups and have been a little indignant about the whole model of "eyeballs are greater than revenue". A lot of what he says makes sense and it has put me in the right frame of mind for understanding them. It was long, but fantastic and I highly recommend reading it.