Windows 8 is still in planning stages,though unofficial transformation packs has been released.
Here are the screenshots of the transformation pack-

Download Windows 8 transformation pack here

A new job has been posted at the Microsoft career site,giving further clues that Microsoft have started working on Windows 8.The job post reads that Windows 8 is in planning and preparation stage.
Here is what the page reads-
Job Category: Software Engineering: Development Location: United States, WA, Redmond Job ID: 701629 7857 Division: Server & Tools Business
This is a great time to join us. Our team owns the Windows Update Client and our code delivers software and updates to over …