Windows Phone 7 utilizes a start screen built from tiles, all of which are dynamic and customizable. Tiles can be used as-is, as “glanceable” heads-up displays to the information you care about, or you can jump into specific topic areas, task-specific destinations, called hubs, by clicking on one. Some hubs include People, Music+Video, and Pictures. You can also promote (“pin”) apps and other things to your start screen. This means that a tile for that app will appear there, and you can of course move it around, positioning it wherever you like. The list of things you can promote is pretty vast. For example, Belfiore pointed out that you can even promote a playlist. And apps? They’re not really called apps. They’re called experiences.
via Paul Thurrott’s SuperSite for Windows: Windows Phone 7 Series Preview, Part 2.