Certainly we have biases towards the authors and in the committees I have participated in the we are quite conscious about the authors and often bring them up when discussing the merits and demerits of each paper. But we should. For one, an author is a measure of trust. Take a lengthy detailed proof about PCPs for instance. You should trust the proof more if it comes from someone like Johan Hastad or Irit Dinur who have histories of dealing with long technical proofs more than someone who is not as detail-focused (like me). But it is much more than that.
A good paper is more than just a theorem and proof. We don't read a paper just to see if a certain theorem is true and if the proof is logically valid. That's just a mechanical check. No, we enjoy the paper because the result and proof have some beauty to it, a clever a new idea or a different way of looking at things. A good paper is a work of art.
Art is not judged in isolation. You don't read a book or movie review that doesn't connect to previous work of the author or director. The price of a painting is greatly affected by the artist who painted it. You choose which symphony or opera to attend more for the composer than the particular piece.
And so it should also be with mathematical papers. I'm not saying we should just accept papers based solely on the authors. No, you must judge the particular work, but you must judge it in its full context and that includes how the paper connects to the authors earlier work, how the work fits in with related work and what kind of theme it follows.
Double-blind reviewing removes critical information, taking away the soul of the paper, the creative forces behind it. History will judge a person's research career through his or her publications so we shouldn't ask that the PC make decisions ignoring the context given from knowing the authors.