I recently came across a the blog of Bill Scott, the Director of UI Engineering at Netflix (http://looksgoodworkswell.blogspot.com/). Bill has some terrific blog posts as well as embedded slideshare presentations that are quite thought provoking about design, functionality and user interaction. Specifically, the presentations by Stephen Anderson is exceptionally done and deliver solid messages. You can view them at: http://www.slideshare.net/stephenpa. I especially appreciate slide #63 in this presentation. It illustrates how usability is about removing friction while psychology is about increasing movitation. This slide was created by Joshua Porter, another great set of presentations if you are interested. Joshua is the Founder at Bokardo Design, a company that specializes in social web app design. You can also find his slides on Slideshare.
One more interesting quote from Stephen Anderson's site:
“You never change things by ﬁghting the existing reality. To change something, build a new model that makes the existing model obsolete.” — R. Buckminster Fuller