There are lots of models of human behaviour, and as the design of systems becomes increasingly focused on people, modelling behaviour has become more important for designers. As Jon Froehlich, Leah Findlater and James Landay note, “even if it is not explicitly recognised, designers [necessarily] approach a problem with some model of human behaviour”, and, of course, “all models are wrong, but some are useful”.
I always like Dan’s in-depth views on these subjects and how he relates them back to design so well. He also details a workshop he did at Interaction 12 Instapaper it up and read it at your leisure. There are lots of links to follow in there too.