Yes, the Mac App Store is officially launching tomorrow (January 6th) worldwide. Similar to the iTunes Store for iOS devices, the Mac App Store lets users browse, purchase, and install software that is sorted by category. Best of all, the installation of purchased software is a one-step process.
According to my sources, the Mac App Store will be available at 12:00 pm (noon) ET on Thursday. That puts it at about 9:00 am PT where Apple is headquartered in Cupertino, Calif.