What is a committee looking for in a dissertation proposal? I've started narrowing down the scope of my dissertation, and I have one year before I need to defend my proposal.  I'm curious to know what is expected from a dissertation proposal.  What are the key elements that I should include / exclude?  What criteria typically used to judge whether the proposal defense is successful?  Are the committee's feedback of the proposal typically used as a criteria for the full fledged dissertation defense?
JeffE is correct; talk to your chair and get feedback. That being said, you'll want to include the following in your talk:


An overview of your research topic
A discussion of relevant literature (to demonstrate that you've researched the topic)
A discussion of your specific problem
Another literature discussion, much more focused on your specific problem
Any preliminary results of experiments you may have run, if any
What you plan on doing for the next few years
(Possibly most important) Any specific issues/problems that your advisors have raised about your research. You should specifically address these to show that you're paying attention to what they say and that you listen to their comments.


The best way to prepare is to talk with everyone in advance and find out what their objections/comments/issues/questions will be as much as possible, and then do your best to prepare for that and any related issues. If that sounds like a lot of work, it's because it is a lot of work.

Dan's comments are also spot on; you may have some very difficult committee members who will ask all sorts of questions, and you should make sure your advisor is on your side from the get-go.