If on my turn I adjust a piece on its square without saying "J'adoube" or equivalent do I have to move it? Suppose I nudge a piece back on to the center of its square using a light tap with the back of my little finger. Will this constitute touching the piece within the meaning of the FIDE touch-move rule?
Article 4.3 of the FIDE rules states:


  Except as provided in Article 4.2, if the player having the move
  touches on the chessboard, with the intention of moving or capturing:


So, if it is clear that my intention is merely to adjust the position of one of the pieces then touch-move does not apply. Of course it must be done on my turn otherwise I am liable to be penalized for disturbing the opponent.

EDIT (2018): The latest 2018 edition of the FIDE Laws of Chess contradict this -


  4.2.1 Only the player having the move may adjust one or more pieces on their squares, provided that he first expresses his intention (for
  example by saying “j’adoube” or “I adjust”).
  4.2.2 Any other physical contact with a piece, except for clearly accidental contact, shall be considered to be intent.


So, if I clumsily brush a piece with my army or knock one or more pieces over this does not count as intention. However if I adjust a piece without saying "j'adoube" or the equivalent then I must move the piece.