> Have you ever heard the phrase “You can’t judge a book by its cover”? (...) it is an empirically observable fact that most people, when presented with a book, will judge it by its cover.

But isn't the phrase "You shouldn't judge a book by its cover"? (And even when "can't" is used, what's meant is often "shouldn't").

Of course people judge books by their cover; they also judge people by the clothes they wear, their height or skin color. Should they?

It depends. Prejudice is our own little Bayesian filtering; it works sometimes but it's not "pure": it tends to have a strong effect on reality (for example, CEOs are mostly of above-average height: not because being tall makes you a good CEO but because we expect tall people to be leaders).

> 99% of geeks will report never having buying anything as a result of an email

bought (just to show that I read at least this far!)