Actually, OSX does support mp3s.
You have two options when exporting from GB, both of which are under the Share Menu.
1) Select "Export Song to Disk." From this menu, you can choose the format to export into (AAC or MP3), as well as the desired quality of the audio. It'll then prompt you for a location to save it to. But I found in personal experience that even though it would export and normalize and all that stuff...I could never find the file. It never seemed to be created. So I started using:
2) 'Send Song to iTunes.' Same deal as before, except it'll prompt you for some info to tag the file with. When it's done exporting, it'll automatically load in iTunes, and then if you want to find it to share with others, or upload to a website, the file will be located in your iTunes music directory, under whatever artist name you chose.
