Check the
wikipedia page on NLP (or
The Skeptic's Dictionary). These links indicate that there are doubts over NLP. However, I am sure that some parts have value. If you watch people's eyes you can definitely observe operations that involve remembering meaning that people have to divert their gaze. Also, thinking from another's point of view (empathetic thinking) is always a good idea. Check the mp3 files linked
here for some auditory channel information on body language and lying from two authors interested in body language and NLP.