http://www.speakingofanimation.com/2010/01/gesture-vs-lip-sync/
"Here’s evidence that proper acting and gestures are more important than lip-sync.
(It’s a clip Pete Docter showed in a lecture a couple years ago.) It works really well and makes me laugh every time.
So make sure your character’s body sells the line before you go crazy trying to get the lip-sync right."