The long wait is finally over as an early build of Windows 8 has leaked. The leak has been posted on a Betaarchive private FTP site and has been confirmed by several reputable sources that it is indeed a legitimate build.
We should note that many of the leaked screenshots showing new features that were published here on Neowin may not be contained within the leaked build. The installer will look similar to Windows 7 but the build is part of the Windows 8 branch.
The build that has leaked is 6.1.7850.0.winmain_win8m1.100922-1508_x86fre_client-enterprise_en-us.iso and is the the final M1 and the last 6.1 build.
Windows 8 is expected to enter beta, possibly as soon as this fall, with OEM availability in late 2012 and possible retail availability in January 2013.