The consensus is that the dissertation proposal defense is more challenging and important than the dissertation defense. The proposal consists of the first four chapters (out of six) of the dissertation. It represents your thinking about the how, what and why of your study. If your committee buys that you have thought it through enough and gives you the green light to proceed with your study, then you are ALL BUT DONE.
My adviser warned me to take a moment before answering questions - he said the questions would get harder and harder. If I paused before answering the questions, then I would just seem thoughtful when pausing for the tougher ones (instead of seeming totally stuck). One of my committee members told me I rocked the Q&A part :) It felt natural - like I was talking about myself. It's like I've been preparing for this moment my whole life.
I met a PhD candidate at a cafe last year. I asked him about his dissertation proposal defense and he said that it was wonderful - you get to talk about the topic that you are most passionate about with a committee of brilliant people. Pretty blissful.
My sentiments exactly. I was a little nervous but mostly excited. Anyone who has ever asked me about my research question knows how I bubble over at the chance to talk about it.
My committee was wonderful. I squealed when they told me that I had passed. I went around the table and gave them all hugs - like how you are taught to do at your birthday party when you open a present if you are a Latina. I was all Latina that special day - June 25, 2013.