The feature, which appears to be only available for “Linked†Windows accounts (presumably to Windows Live), allows for users to “roam†to different computers and devices with their various settings and configurations, automatically applied.
The range of settings for roaming include the desktop wallpaper, Aero glass colour, accessibility options, language options, applications settings (probably only for AppX packaged apps), Windows settings and Wi-Fi profiles and Windows-managed passwords.
As someone who uses both a desktop and laptop, this is clearly going to be one of the killer features of Windows 8.
This looks like a great new feature!