By default Windows 7 will permanently consume a chunk of your hard drive with its hibernation file, but if you never use sleep, and always turn your PC off, then this will never actually be used. To disable hibernation and recover a little hard drive space, launch REGEDIT, browse to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Power, then set both HibernateEnabled and HiberFileSizePerfect to zero.
