As you know yesterday Windows 8 Developer Preview was released at BUILD and is also available for download.
Windows 8 Guide – Windows Developer Preview
Check out this Free ~40 pages booklet covering a bit of basics in what’s new , something for developers about Windows Runtime and app model. Fundamentals, devices and security and a bit on Windows 8 for business.
Microsoft Windows 8 Developer Preview Fact Sheet September 2011
Also a factsheet has been released by Microsoft.
Download this Word file (.docx) from here and learn more about Windows 8 .
Download link .