Stereotypes: can we judge a book by its cover?

Stereotypes surround us, they are involuntarilly stick to our minds. For example, the Bristish are said to be extremelly polite.

Can you name some other national stereotypes? What about the Spanish? An article written by a British about "how to be Spanish" has been recently hardly criticised by Spaniars. What is your opinion? Read these more pleasant ones: 1, 2, 3. 

Therefore... can we judge a book by its cover? Can we rely on racial, gender, religious or any other kind of stereotypes? Children are undoubtelly certain we are all equal.