With all the bench marks of the A8X coming in close to MBAs and MBPs of a few years ago, I am convinced Apple is working towards building an ARM-based Mac portable.
That would be fantastic indeed. My Macbook Air is my main computer, over 2 years old but still going strong (except the battery only has half capacity now... I might have to take that "service battery" more seriously). I love how it's silent, the built-in speakers and display are flawless, keyboard and trackpad are comfortable.
A tablet running full OS X would be very cool, especially with a keyboard-dock for being productive.