Is prayer effectively second-guessing God? If one were to accept that God has a plan and that His will is to be honored, isn't hoping to sway God's plan for the future disrespectful?

-- Update --

A lot of these answers are across the board, so here's an example to help refine the question:


  Someone's wife is gravely ill and in the hospital, and her church's
  parishioners say they will "keep her in their prayers".


It's safe to assume that they will pray for God to reverse his direction regarding her health and make her better, and it's also fair to say they're not asking him to show them the way to do it themselves.

Just making a request for him to rethink the matter, it seems. Where does that fall?
I think the following explanation of prayer is very helpful:


  Prayer
  
  Prayer is the act by which the will of the Father and the will of the child are brought into correspondence with each other. The object of prayer is not to change the will of God, but to secure for ourselves and for others blessings that God is already willing to grant, but that are made conditional on our asking for them. Blessings require some work or effort on our part before we can obtain them. Prayer is a form of work, and is an appointed means for obtaining the highest of all blessings.


So we don't pray to change God's will, we pray to learn about it.


  Matthew 7:7 (KJV)   
  
  7 Ask, and it shall be given you; seek, and ye shall find; knock, and it shall be opened unto you:


But yes, trying to change God's will is disrespectful. You're essentially saying that you are wiser than God.


  Romans 11:34 (KJV)   
  
  34 For who hath known the mind of the Lord? or who hath been his counsellor?