According to an official blog post for Windows 8, the 'F8' keystroke event has been removed and will not be supported by the new operating system. Hardware and software improvements in Windows 8 have drastically reduced the time for Windows 8 to respond to the 'F8' keystroke; hence, its removal from Windows 8 is simply natural progression to make user experience better in this new iteration of the operating system.
Besides the removal of support for 'F8' keystroke, the classic, keyboard-driven options menu has been done away and in its stead, there is a redesigned Metro-style GUI. This redesigned boot option can be invoked from the computer's UEFI BIOS or from Windows itself by the user, however, when Windows 8 detects any issues during its boot-up, it will invoke the redesigned boot option for user intervention.
The redesigned boot menu also allows the user to access a menu, "Advanced Options", with quick access to System Restore, System Image Recovery, command prompt and Windows 8 startup settings. Due to the fast boot up time of Windows 8, the engineers at Microsoft have had to re-work the way users can access the boot menu without the need for keystrokes, this makes logical sense as Windows 8 will also be powering devices that only have touch interfaces.