I have a 2012 MBA. I find myself taking my iPad on my shorter trips, especially since I can work from Dropbox or Evernote. I do not see this new MBA as replacing my current one. I feel I have already won my chase for "thin and light."
This would work if it did not interrupt G's current revenue stream- not sure how the rates would be set for the advertisers- especially smaller ones who need high target niched key words.
I am much more complex than my search history- I find that "relevance" to me can depend on things as diverse as my current mood. I too am torn because I know that increased relevance means I am giving away more and more of myself- I'm pretty sure that G has no limits in this pursuit of "relevance."