If you intend to upgrade to Windows 8 soon, you will need to do so in January, as the $39.99 price for the Windows 8 Pro upgrade will expire on January 31. You can also purchase the upgrade now and install it at a later point in time. The shipped and packaged version is priced at $69.99. The offer includes about $70 in discounts for certain apps.
Microsoft will also phase out the free Media Center upgrade for Windows 8 Pro on January 31. Windows 8 users have to purchase the software for $69.99 (and get an upgrade to Windows 8 Pro).
Users who purchased Windows 7 PCs with a discount offer for Windows 8, will have to upgrade also by January 31. The $14.99 offer will not be available in February.
Those who are still using the preview version of Windows should also slowly migrate to a different version, since the software will expire on January 15.