ZDNet UK - News - Another survey rates Microsoft cheaper than Linux
I'm as sceptical as the next anti-M$ person, but the fact remains that linux on the desktop PC isn't in the market. Where I see it potentially making headroads is through the network admin and applications markets. Most corporate users use maybe 5 apps on their systems. If you remove the need for these apps to be MS-based, users don't care which desktop they're running. But IT managers still do, so you need to beef up the enterprise desktop admin tools too.
Then, who cares what OS you're running? That's how it always should have been. To use your car analogy, who cares what engine management system they have in their car? Most people don't even know.