Nowhere at present, which is hardly surprising, they only started the move in Jan 2006. It takes a whole world of hurt to change instruction sets and compilers to run independently on any intel chip in that manner. I'm sure they will do it in the end - would be suicidal not to now they are going down the Intel route.
I agree, it probably will halve overnight, hence my keeness for Apple to suceed. I am not an Apple or MS or Intel or Linux or whatever Fanboy, each has their target market. Competition is a wonderful thing, as it hurts the bottom line - nothing like the latter to galvinise innovation, and we need innovation in the PC world.
Apple made the same mistake as Betamax in the old VHS / Betamax wars - they got the marketing wrong, and we were stuck with one technically inferior standard and reduced innovation. I hope Apple dont make the same mistake twice, I dont think they will, iPhone marketing has been exemplary so far. I'm hoping in 10 years time there will be three out there Windows, Linux and Mac fighting for the same market space. It'll take that long for the Mac and Linux to get to the stage of seriously challenging the PC space, and I hope they do - then we will see the sparks fly