It appears that SpeedFan has been updated to version 4.49, making it fully compatible with Windows 8 and Windows Server 2012. This update also includes improved ACPI support. Here are the key points mentioned in the release notes for SpeedFan version 4.49:
Full support for Windows 8 and Windows Server 2012.
Improved ACPI support.
Version 4.49 replaces version 4.48 due to a typo that caused ACPI temperatures to be reported incorrectly on some Windows 7 systems.
Changes to the installer naming schema to address an issue where Windows was reporting the wrong version to SpeedFan's installer.
Both the installer and the executable are now digitally signed with the company's (SOKNO S.R.L.) certificate. You can find more information and download the updated SpeedFan version from the official SpeedFan website: http://www.almico.com/speedfan.php