Refactored to focus and bring out the really good sections.

There are some really good sections in the intro, and to bring them out more I rearranged the page and moved some of the Hadoop text to the vs-hadoop page. Most people will glance at intro pages (if they even land there ... see Google), and giving them the sexiest and most succinct info (i.e., the Key Features bullets) up top will help them quickly digest what's most salient (i.e., why should I really care). The following why/when/etc. are great too for those who get pulled in.