Hmm:

• At the Windows logon screen, you're actually logged into an account called SYSTEM - as far as privileges is concerned, it has about the same amount of rights as a Power User
  
• A lot of text/images can be changed by resource hacking - for example, the Start menu text can be changed by resource hacking explorer.exe
  

Damn, can't think of any other stupid ones (I learnt most of this from my days of hacking XP By the way :P)

Some, probably, more useful ones:

• The Windows key is pretty awesome - hitting Win+E brings up explorer :P
  
• If the setting is enabled, a key combination will crash Windows (can't remember which, but it's like pressing the Pause key twice or something)
  
• Make new folders often?  Try (in explorer) hitting Alt+F, Enter, Enter...  (obvious, but a very useful shortcut)