The recent Government Computer News group shared a good write up on the changes associated with the new Metro UI and several more detailed informational links are included from the “Building Windows 8 blog”
Windows 8 – New Metro UI and start screen
QUOTE: Microsoft went a step further than that with the Windows 8 design and laid all of the programs out in a single view on the Start Screen, dropping the taskbar altogether from the Metro UI. That layout, in Microsoft’s view, represents “the evolution of the Start menu.” In this case, “evolution” means a collection of square and rectangular colored tiles, representing programs, all sitting right on the desktop screen.
Next, Alice Steinglass, group program manager for the core experience evolved team, took up the cause of explaining the Start Screen’s design in Windows 8. Her main point is that the Windows 8 Start Screen functions as a sort of “dashboard that helps you stay up to date and connected in a high quality experience substantially improved over the notification tray.” The notification tray on the taskbar was simply dropped in the Metro UI because it just added clutter to the desktop. Similarly, Microsoft dropped the folder approach in the start menu because “folders are a way of burying things, not organizing them.”