Microsoft will apparently be doing something a bit different with the upgrade packages prior to the release of Windows 8 which should help alleviate the drop-off in PC sales that normally accompanies a major OS release.
Microsoft will make the so-called "Windows 8 Offer" available to consumers buying a Windows 7 PC running Home Basic or higher, allowing them to obtain Windows 8 Pro once Windows 8 is available. The Windows 8 Pro SKU is for tech enthusiasts and business/technical professionals, and includes encryption, virtualization, PC management and domain connectivity, as well as support for a separately priced Media Pack for Windows Media Center.
Seemingly because the offer is for the more feature-rich Pro SKU, rather than the entry-level Windows 8 (consumer) one, the offer won't be "free." There will be some fee attached to the coupon, but there's no word on what that's going to be (so far). The upgrade offer will start on or around June 2, 2012
Although pricing hasn't been announced, it looks like you may be able to get a PC with a version of Windows 7 Home Basic, yet be eligible for an upgrade to Windows 8 Pro. That could be a cheaper migration path that might make a lot of sense for PC buyers who would otherwise hold off on their purchases.