Valve has updated Portal.   The updates will be applied automatically when your Steam client is restarted. The major changes include:

• Fixed screen \”fuzziness\” caused by color correction operation
• Fixed text not rendering in game if font Tahoma was disabled
• Fixed startup video not playing fullscreen
• Added optional -snd_openal command line parameter to force the engine to use the OpenAL api, can be used if Portal is playing no audio when launched normally
• Added mac_fsbackground convar, on Snow Leopard or better you can set this to have Portal still visible when it is not the foreground application