From what I have read, the Intel based Macs are supposed to be able to run Windows, which means that they don't have too much customized hardware under the hood. That implies that getting OS X to run on Intel machines is going to be mostly one of getting your hands on the right drivers and on the OS itself.
I expect this to turn into a fight for Apple as they work to block independently developed device drivers. And given that Darwin is open source, it is going to be hard for them to stop.
Apple will have to watch the selling of OS X closely also, something they can do much easier. But if it becomes popular, Apple is sure to have grey and black market problems with that also.
Apple faces a basic catch-22 here in that part of their popularity is built on their control of the hardware. The more popular they become the harder it is for them to control the hardware. Thus becoming more widespread is going to interfere with one of the things that makes them popular to begin with.
Jay