Windows 8 has a new hotkey combination that lets you take and save screenshots instantly. To take a screenshot, hold the Windows key down and press the Print Screen key. Your screen will flash and Windows will save a screenshot to your Pictures folder as a PNG image file.
You might assume that WinKey+Alt+Print Screen would take and save a screenshot of the current window, but it doesn’t. Maybe this will be implemented in the final version of Windows 8.