As the earlier build of Windows 8 Milestone 1 Build 7850 has been leaked, it is expected that the new features of Windows 8 will be dig down. A new feature has been discovered by the experts called the Windows Portable Workspaces. Portable Workspaces enables the users to create portable Windows 8 on their USB drives or any other external storage device.
This feature seems to be available for enterprise users only as the portable workspaces feature is available in Windows 8 Enterprise Edition. More information about this feature is yet to be explored but you need atleast 16GB of storage to install and run Windows 8 Portable. You can learn more about this feature in the following video: