What is meant by "Get behind me Satan"? Considering
Matthew 16:23: 

Jesus turned and said to Peter, "Get behind me, Satan! You are a stumbling block to me; you do not have in mind the things of God, but the things of men."

Why did Jesus choose the "Get behind me Satan" phrase here?  Is there context for this elsewhere in the gospels or in the Bible?
In context:


  21 From that time forth began Jesus to shew unto his disciples, how
  that he must go unto Jerusalem, and suffer many things of the elders
  and chief priests and scribes, and be killed, and be raised again the
  third day. 22 Then Peter took him, and began to rebuke him, saying, Be
  it far from thee, Lord: this shall not be unto thee. 23 But he turned,
  and said unto Peter, Get thee behind me, Satan: thou art an offence
  unto me: for thou savourest not the things that be of God, but those
  that be of men.


The context here is that Peter was suggesting that Jesus take a course of action other than the one that He was predestined to fulfill.  Jesus knew His destiny, and he knew the will of the Father.  What Peter was suggesting was that Jesus go against the will of the Father.  

As such, Peter's words were the words of an adversary of God.  Not consciously, I'm sure.  I have no doubt that Peter sincerely didn't understand what he was suggesting - He just wanted Christ to live.  He loved Jesus, and didn't want to see Him die.  Nonetheless, his suggestion was in direct opposition to the will of God.  The word translated Satan here is usually applied to Satan as we think of him, but it literally simply means "adversary".

From Barnes' Notes on the Bible:


  Get thee behind me, Satan - The word "Satan" literally means "an
  adversary," or one who opposes us in the accomplishment of our
  designs.
  
  It is applied to the devil commonly, as the opposer or adversary of
  man; but there is no evidence that the Lord Jesus meant to apply this
  term to Peter, as signifying that he was Satan or the devil, or that
  he used the term in anger. He may have used it in the general sense
  which the word bore as an adversary or opposer; and the meaning may
  be, that such sentiments as Peter expressed then were opposed to him
  and his plans. His interference was improper. His views and feelings
  stood in the way of the accomplishment of the Saviour's designs. There
  was, undoubtedly, a rebuke in this language, for the conduct of Peter
  was improper; but the idea which is commonly attached to it, and
  which, perhaps, our translation conveys, implies a more severe and
  harsh rebuke than the Saviour intended, and than the language which he
  used would express.


This is also the understanding in Clarke's Commentary on the Bible:


  Get thee behind me, Satan - Υπαγε οπισω μου σατανα. Get behind me,
  thou adversary. This is the proper translation of the Hebrew word שטן
  Satan, from which the Greek word is taken. Our blessed Lord certainly
  never designed that men should believe he called Peter, Devil, because
  he, through erring affection, had wished him to avoid that death which
  he predicted to himself. This translation, which is literal, takes
  away that harshness which before appeared in our Lord's words.