Windows to Go allows for the creation of a bootable Windows 8 Enterprise installation on select certified media. The Windows to Go workspace can be booted on any hardware with a USB 2 or USB 3 port, regardless of the operating system installed on that hardware, and enables the ability to “roam” on up to five different PCs. Windows to Go workspaces can run key new Windows 8 features such as Client for Hyper-V, directly from a USB thumb drive and can serve as a work from home device by running corporate compliant client images.
More information on Windows to Go can be found here: http://technet.microsoft.com/en-us/library/hh831833.aspx
NOTE: Windows to Go is not supported on Apple-based hardware as described here: http://support.microsoft.com/kb/2746182