Apple has announced the official launch of the Mac App Store on January 6th, 2011. The Store will be available in 90 countries at launch time. The new store will feature free and paid apps in Education, Games, Graphics and Design, Lifestyle, Productivity and Utility categories. You can purchase, download, install and use the apps with one click just like on iOS devices like iPhone, iPod Touch and iPads.
The Mac App Store will be available to OSX 10.6 (Snow Leopard) users through Software Update as free download on January 6th, 2011.
For more info, please see Apple's press release.