Windows 8 Consumer Preview Weather App seems to always default to Fahrenheit, and it may be not immediately obvious how to change to Celsius:

• Open the Weather App
  
• Open Side Panel Charms (drag mouse cursor to the top right corner or press WIN+C) 

Read more: Windows 8 weather app - change from fahrenheit to celsius

If you are not worried about security you can make Windows 7 login automatically using your chosen account even if the account is password protected.

• Start > type netplwiz and press Enter
  
  
• User Accounts window will appear
  
  
• Select user you want to use for automatic logon
• Uncheck "Users must enter a user name and password to use this computer"
• Press OK
• Enter your password if prompted

Next time you restart your computer Windows will login automatically using the account you selected.

Windows XP by default keeps some important files and folders hidden. This is to protect files from accidental deletion, but if for any reason you want to see such files it only takes a few seconds to change this default behaviour:

• Open your "My Documents" folder (in fact it can be any folder)
• Click on Tools > Folder Options
  (In Windows Vista and Windows 7 you may need to press Alt key to display the top menu bar)
  
  
• In Folder Options dialog click on View tab
  
  
• To show hidden files select "Show Hidden Files and Folders"
• To show system files uncheck "Hide Protected Operating System Files"

Windows  7 Start Menu Search feature helps you to find data on your computer, but it's easy enough to make search the web as well.

 All is needed a little registry change:

• Open registry editor - just type regedit in the start menu search bar and click on regedit.exe)
  
  
• Navigate to: HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\Explorer
  If Explorer or other Key doesn't exist, simply create them by right clicking on the existing key above and selecting New > Key
  
  
• Inside Explorer create a new DWORD type value:
  Name: DisableIndexedLibraryExperience
  Value Data: 1
  
  
• Restart computer

Now, when you start typing in the Start Menu Search bar you will see an option to Search the Internet which will open your default Internet browser and perform a search using your default search provider (Google, Bing, etc.)