9to5Mac apparently snuck its way into the Mac App Store a little early (the marketplace is set to open up on January 6), and has brought back some screenshots of the app's OS X trappings. You can see the app's icon already, and the app will have a login screen very similar to what you already use in iTunes to install iOS apps.
Parental controls are available in the store's preferences, and various installs will all be handled by another app called "store helper." Those controls are configurable for various ages, so you'll be able to define if you want apps to run for users over 4, 9, 12, or 17.
Unfortunately, The Mac App Store won't support Game Center or in-app purchases at launch, but given the growing popularity of both of those elements, that may change in the future. We're inching ever closer to the Mac App Store's release, and developers are undoubtedly working even over the holidays to make sure their apps are ready to go at launch. It should be a nice way to kick off 2011 for Apple.