All I have to add is that the story of a prominent Mac user switching to Linux after frustrations with lost data and proprietary formats is a fairly familiar one.
Hacker with bullhorn: "Save your money! Accept one of our free tanks! It is invulnerable, and can drive across rocks and swamps at ninety miles an hour while getting a hundred miles to the gallon!"
It did seem fairly obvious that OS X's Unixey goodness would take a bit of wind out of the sails of Linux on the desktop, but I figured it'd continue to move forward -- and Ubuntu seems to get closer with each release to that threshold of actual usability for normal people.
Apple seems to have learned how to compete against "good enough, but cheaper." Actually, it might be the Windows guys who should be concerned -- you don't get much cheaper than "accept one of our free, invulnerable tanks," and Ubuntu is making that high-tech super-tank easier and easier to drive.