Beginning June 2, 2012, consumers who purchase up to five new Windows 7 PCs preinstalled with Windows 7 Home Basic, Home Premium, Professional, or Ultimate will be eligible to purchase an upgrade to Windows 8 Pro upon general availability of Windows 8. Qualifying purchases must be made before January 31, 2013, and offers must be redeemed by February 28, 2013.
Microsoft wants to make sure that you still buy computers over the summer and not wait for Windows 8. Buying a Windows 7 PC starting tomorrow gives you the option to upgrade to Windows 8 Pro for $14.99 once it is available in Fall.
Unlike previous upgrade programs, Microsoft will manage the redemption process, including eligibility verification, payment, software delivery, and support. Delivery of Windows 8 Pro will occur via electronic software distribution.
See also the Windows 8 Upgrade Offer site.
As reported, you can now download the new Windows 8 Release Preview.