Updates to the Steam Client have been released. The updates will be applied automatically when your Steam client is restarted. The specific changes include:

Steam Client

• Friends now displays the game you are playing to all your friends
  
• Attempting to add a Friend who doesn't have a Steam account will now give you the option to send them an email, inviting them to become one
  
• The words 'valve' or 'steam' are no longer available for use in the Friends name
  
• Fixed game install dialog over estimating install size for games that shared content
  
• Added a "Don't Show me Again" checkbox to the System Requirements dialog for games
  
• Fixed FPS drop after running a listen server

Note: There was initially a Counter-Strike 1.6 crash caused by this update, but that has since been fixed.

News Source: Steam News