Here. Besides the cool scenarios BillG mentions that that Longhorn will enable, I like his answer to USA Today asking how long it will be before Longhorn is available:
"Years. At this time we're doing the prototyping — feasibility studies, performance studies. We don't have a date because what we have is a technological breakthrough that we have to really make sure we refine and get right. Then we'll get to the point where we'll set up an engineering schedule."