We have recently posted that Windows Server 2012 Release candidate has been available for download, now the client version of Windows 8 is available for download on Technet and MSDN.
Here are the details of the files-
Windows 8 Release Preview 64 bit
Size: 3353 MB
Windows 8 Release Preview 32 bit
Size: 2494 MB
We would be posting the links here once it is available for download on public servers.
Update: Everyone can download Windows 8 Release Preview from here- http://windows.microsoft.com/en-US/windows-8/iso