Microsoft StartKey will put your entire Windows desktop on a USB Flash drive including the software programs, files and settings.
You can then plug this USB stick into any PC and use it as if it were your own personal workstation.
While this is not a new concept and existing applications like MojoPac do offer similar functionality, Microsoft Startkey will definitely help in popularizing this whole idea of converting a portable storage device into a computer, especially among the non-techie crowd.
The first public beta of StartKey is expected later this year. For more on Windows Startkey, check out ZDNet.