The scenario: you have the Windows 8 Metro-style UI but you wish to disable it and revert to the Windows 7 style desktop and Start menu. Here are instructions to edit the Windows 8 registry.
Update 1: While this worked in the Developer Preview, it is not working in my Windows 8 Consumer Preview.
Update 2: The latest plan is to create a shortcut to Explorer in the startup folder.
Now change: RPEnabled from 1 to 0 (zero). See screenshot below.
The old Windows 7 style Start menu and desktop appears immediately in Windows 8. However, if you change RPEnabled back to 1, then you need to logoff / logon before the Metro UI returns.
Note: Unlike the Developer Preview, this did not work in the Consumer Preview.
The big mistake is navigating to the wrong hive in the registry, people go the HKLM when they should start in HKEY_Current_User, as shown in the above screen shot.
Here is another take on getting the old style desktop.
I read with interest of the registry hack TaskUIEnabled. However when I got the September 2011 Build version, I could not get this setting to work.
Conclusion: This is one registry hack not worth bothering with.
Registry Instructions to Enable the Modern Windows Task Manager.
Create a new DWORD 32-bit value called "TaskUIEnabled"
Setting its value to "1" enables the ribbon. Zero would turn off this feature.
My favorite technique for recovering from registry disasters is to export the registry section before I start experimenting. To follow my example, launch regedit then click on the File menu, Export, Selected Branch.