About time, I think
When Apple started making their own ARM chips, I predicted that they would move to ARM on the Mac line also. It has taken longer than I expected, but Apple has good reasons for this:
1. It would make Macs the ideal tool for developing iPhone software, as it can be made to run it without emulation.
2. More parts of the OS can be shared between Mac and iPhone.
3. It allows Apple to make a SoC to exactly their specifications instead of relying on what Intel produces.
4. It removes dependency on Intel (or AMD).
It is not impossible for Apple to make a 64-bit ARM processor that will outperform the fastest Intel processor. I'm sure Apple would love having the fastest laptops around, so people would migrate from Wintel to Apple for performance reasons. Apple need to do more work on the FP side to make this happen, but it is not impossible.