Windows 8 – Hiding the Start Button
Recently, images from a newly compiled Windows 8 build were posted on a Chinese forum. In these builds the Start Button is hidden by default which was not the behaviour in the Developer Preview. However, after poking around the Developer Preview it is apparent the folks at Microsoft were at least thinking about this behaviour from an early stage, with a registry switch being available.
You can toggle the switch by heading to the registry path: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer, creating the a new DWORD named YouBettaHideYoPearl and setting the value to 1. After restarting Explorer or logging off & on the settings will be enabled, you can undo this by either setting the registry key to 0 or deleting the key.
After enabling this behavior, you can make the Start Button temporarily reappear by hovering your mouse over the bottom left hand corner of the Taskbar, if your into mouse movements.