performance per watt is not just integer operations per second, that is floating point operations as well, which we know current Arm processors do not do well.
I believe Intel has always maintained that they have the advantage in performance per watt, but the power consumption was too high for mobile because of leakage, meaning idle time was killing the battery.
Not true with 22nm Tri-gate which will have 10x power savings while idle. ------
ARM is much better at performance per watt (which is the appeal to use ARM in some server workloads). Yes, ARM (at least the A8) is rubbish at floating point.
Leakage is an issue but Atom is a power hog when running anything (which is now more of an issue with smart phones as they are used more than dumb phones).