How much does body language influence people?

We all have a certian way of walking, standing, sitting, ect. This can be affected by our mood, physical state, and other things. Most of the time I’d imagine that we are not even aware of these things, but that they probably DO affect us subconsiously. My question is, how much influence does body language have on people (and where can I learn how to take advantage of this)?

Well, in my pursuit of a Communication degree I remembered my teacher saying several times that our nonverbal communication does affect us. Consciously as well as subconsiously. I can scrounge around for some of the books or links if you want.

There is a lot written about body language, such as http://www.johnmole.com/articles18a.htm
http://www.worldtrans.org/TP/TP1/TP1-57.HTML
http://www.collegegrad.com/jobsearch/15-8.shtml

I believe that interviewers and interrogators use it both to interpret their subject’s actions and to also “play” them. I guess you could search online or look up books on the subject. Probably courses offered, too.

Veeerrrryyy Innnnnnteresting. Thanks for your help :).