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About 20% Windows XP SP3, but only for watching Blu-Ray movies from Netflix. If/when OSX adds Blu-Ray playing support, that fraction will drop down to 0%, which is one reason I really really want Apple to stop dragging its feet on Blu-Ray.

This changes when I'm on the road, because then I often use Remote Desktop (either via VMWare Fusion or Boot Camp) to tunnel into my office WinXP computer.
 
Slightly off topic from the original question, but what size partition are you guys giving Windows 7 64 bit? If they ever launch the new MBPs, I'll be going this route more than likely.
 
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