Ultra-Mobile PC
This thing is amazing!
It runs Windows XP (Vista once that ships) and all apps that run on Windows.
Check out the experience (the UI, apps, etc.) at https://www.microsoft.com/windowsxp/umpc/seeit.mspx
Check out the devices at https://www.microsoft.com/windowsxp/umpc/hardware.mspx
And it looks like you can buy one in April!