There seems to be a contradiction in his argument. He talks a lot about the signup pages, focusing on what he guesses is Tumblr's much higher conversion rate and the reasons for why that conversion rate is high. Shortly thereafter, he lays into Posterous for being too metrics-driven. How could a company that's too metrics-driven let themselves get crushed (again, according to the author's guess) on something as important as signup page conversions?

The whole piece has this arbitrary anti-Silicon Valley animus that I don't really get and which doesn't seem to serve any purpose.

It's useful to talk about conversion rates, the importance of good UI/UX, and what Tumblr and Posterous do or don't do well, but the broader, hand-waving indictment of Silicon Valley doesn't add anything.

(Also, the author doesn't directly do this, but articles like this can falsely suggest that the two companies at hand are playing a zero-sum game.)