The Windows 8 boot experience will reflect the personality of Windows; it will be fast and fluid, seamless, and beautiful every time. By leveraging the capabilities of UEFI and working together with the ecosystem, our goal is for the PC to power up to the manufacturer’s logo and stay on that screen all the way from POST to Windows logon UI. The logo should be beautiful and reflect the brand you trust when you purchased your PC. Firmware renders the logo during POST, the logo persists on screen when Windows boot takes over, and remains through OS boot. In effect, we are bridging two experiences (firmware + operating system) to deliver one experience, as you see here...
Full details over at MSDN.