Hacker WZor has released a collection of screenshots from what appears to be a 'Microsoft Confidential' build of Windows 8.1 Update 1. The update is officially planned for an April release.
One of the interesting thing about the screenshots is that it seems Microsoft is adding the ability to pin Metro applications to the legacy taskbar. This would allow users to launch Metro apps from within the desktop, instead of having to go to Start Screen first, however it is not clear if these apps will be able to run in a desktop envrionment or not.
Wzor also recently claimed that Microsoft's next operating system, Windows 9, will reach RTM by October 21 of this year. This may probably the quickest Microsoft has moved from one OS to another, with Window 8 releasing only two years ago.