I have a mac and a YPG635. There are MAC midi drivers but not much else. The story I have heard is that Yamaha had a falling out with Apple so the official Yamaha software to push files to the keyboard (Music Downloader) and the Yamaha version of "Itunes" that lets you buy there music, does not run on MAC.
You can hook the MAC to keyboard with a USB cable (like a printer) and play tunes from midi files on the MAC or a midi editor.
