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

Portal
  • Performance improvements
  • Fixed crash during offscreen rendering
  • Fixed overbright screen when rendering with Radeon X1x00 on 10.5.8
  • Fixed subtitle mode to not include sounds, use close captioned mode for that functionality
  • Fixed achievement awarding being delayed to map change
  • Fixed view jumping when coming back from the in-game UI to the game
  • Improved support for using the Command key as a key bind