Via DownloadSquad, Netflix is beta-testing a new online streaming video player based on Microsoft Silverlight that now allows Mac users to instantly watch Netflix movies on a Mac once silverlight is installed. PC users have enjoyed this ability for sometime and the new player is merely an update. Because this is a beta test, you have to opt in if you want to use the new services.
According to Netflix, they do warn users that when choosing the Silverlight player, users will have to use Silverlight to watch Netflix movies on all the users' computers. Additionally, they mention that the selection of movies is more limited.