That Cortex A15 review indicates that performance will be on par with a 2Ghz Core 2 Duo (3-issue superscalar 15-stage pipeline). Although Intel achieved this performance over 5 years ago, the chip is admirably about half as fast as the very fastest processors at serial processing (typical of laptop processors) which comprise the vast majority of applications. At 32nm the ARM processor could be expected to do so at around 5 watts per core at peak, opening the way for speculation of its debut in the Mac Book Air.
Charlie at SemiAccurate seems to think it a certainty, though betting on a successor to the A15 somewhere around 2015 (this was also speculated about a year ago as well).
The processor wars are heating up thanks to the increased importance of power efficiency. If things continue to go the way they are, I wonder if the DoJ will end up allowing ARM to acquire AMD?