PLEASE READ: When trying to install the theme, I've received the following message: "The package could not be installed. The theme is missing the style.css stylesheet."
It's ok, don't panic... when we submit the theme to the marketplace we have to submit all of our files. The zip you downloaded doesn't just contain the theme, it contains Help Documentation, Licence information and the theme itself.
Simply extract/unzip the zip file the marketplace gives you, you'll then find a 'Theme' folder, in there will be the theme zip file you need to upload to WordPress.