Agreed. Within my own field, there are less than 10 people who are presently working on the same topics as I do. Consequently, we are constantly asked to review each other’s papers, and it is pretty trivial to tell who the author is, either because of the views and interests shown in the paper, or because of language use (i.e. you can tell that the author is a native speaker of the language in which the paper was written, or from their unidiomatic skills in it you can often guess at their native language).
The hard part in this is remaining silent and pretending you don’t know anything about this, when you meet your peers at conferences.
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...
The hard part in this is remaining silent and pretending you don’t know anything about this, when you meet your peers at conferences.