Here is an app for those who absolutely hate Metro in Windows 8, but are forced to use it. The select group of course includes those who want to develop for Windows Phone 8, which needs the Hyper-V feature to run the emulator.
Ex7forW8 is a wrapper for the Windows 7 explorer, which means the Metro start screen is completely abolished and not even loaded which means absolutely no RAM or cycles are wasted.
New Windows Explorer features like ribbon and file copying are however preserved.
The hack can be used on Windows 8 or Windows Server 2012 RTM or RP versions, really any Windows 8 version.
This program does not modify system files and system protected registry entries and you can switch back to unaltered Windows 8 UI any time. Windows 7 shell is enabled only to users which switched to it and other users can use Windows 8 shell without any problems.
WindowsPhoneHacker, who recommends the app, reports no significant issues, so if you truly want to kill Metro read more about the app here.