The idea that liberals are more likely to choose the Mac platform has been around for a while. I had always thought that it was probably because creatives are over-represented among Mac users, and liberals are over-represented among creatives. But Kevin Drum goes to a progressive conference and reports that about 70% of the laptops are Apple. There might be more to this than that.
Maybe it's because living in Mac-land is like living in a socialist utopia. Everything has been pre-planned and designed for your comfort. Owning a PC, on the other hand, is like being stranded in a capitalist jungle: products are sprouting everywhere, dangerous tropical viruses are in the air, lots to eat and lots to be eaten by.
UPDATE: Drum says Apple has a 4% market share. That's true of computers in general, but they have a much stronger position in the laptop market: around 12%.