One of my favourite shows is Babylon 5. In it, a character, with suspicious motives goes around and asks people this very question, "What do you want?"
It is such a powerful question, in what it reveals. Some people might answer it in terms of objects, wealth, our outcomes. But for some people, it is a question that is asked in the wrong context.
Walk into a store - "What do you want?" ... well, most people would think that is a rude - depending on the tone of course. Answer the phone with "What do you want?" and measure the person's reaction.
But if you ask this question in a genuine and caring manner, THIS is when you get to truly know people's motivations, and desires, and I'm so glad the people in your life saw it that way and not a pissed off "What do you want?"
That, or at least you've got the ability to modulate it properly :P
And regarding me rambling about one of my favourite shows, this is such a good scene:
RE: what do you really want? update