From daringfireball.net. We already know that Mac OS X's market share in laptops sold to home users (i.e. not companies) in the age range 19-25 is huge. Ubuntu and related open source (ubuntustudio) is only one step sideways from Mac OS X. Notice the clever statistical spin here, "9 out of 10 dollars". So maybe only 70% or 60% of volume.

Mac and iPhone