I have a Mac with Snow Leopard, and a Casio keyboard with MIDI interface. Before both worked together, I have so happily adjust all afternoon my keyboard to the correct channel to configure the MIDI interface with utilities from the Mac OS and to dig into the settings of GarageBand. What I did not know - the 'Midi In "cable is included in" Midi Out "on keyboards, and vice versa. Since I am a beginner, I knew that he does not (I suppose it's always like that and no fault of my keyboards or cable, but I do not know). It works now. In retrospect, I have to say that the driver is automatically detected correctly, so it is Mac compatible.
Five stars because it does what it should and not annoying me otherwise.