You can spend your whole day on the desktop and forget the Metro UI ever existed.
How do I do that? Sure, I can get to the old desktop, but it's just a desktop with not much on it. If I actually want to start a program, as soon as I hit the Windows key, it switches back to the Metro start screen. So unless I'm expected to put icons for all my programs on the desktop or pin them to the task bar, I'm going to have to use Metro. That said, the start screen doesn't seem much different than putting icons for all my programs on the desktop, and feels like a regression from the Windows 7 start menu--I installed SQL Server 2012 and Visual Studio 2012, and instead of organizing the SQL stuff in one folder and the Visual Studio stuff in another folder, my start screen now has almost two dozen tiles on the right, with really pixelated/ugly icons for the SQL 2012 stuff, and no distinction between the SQL tiles and the VS tiles. E.g., there's something labeled "Project Conversion..." is that SQL or VS? Sounds like it might be a Visual Studio thing, but no, it's actually the SQL Integration Services Project Conversion Wizard.