It is not blind for most science fields (I was not aware of any that were blind before reading this. PhD in Earth Science). What fields do you know of where journals send out papers for review with the author and his/her affiliation removed?
I've seen it exactly once (in a numerical analysis journal). Authors were blacked out. This was undermined almost immediately when the authors wrote in the introduction "... following previous work of the present authors [1]...".
Even if all these clues could be effectively removed, the nature of the research work, tools used, writing style, all unambiguously indicate authorship to someone in the field. I think for this reason double-blind review is not popular.
Which is not to say that it would be great if it were possible...
