Guys. There is much more to embedded devices than just lowering CPU wattage, slapping it in a Phone and boot. Take for example system-on-chip designs. What made ARM ubiquitous in the embedded arena exactly is that it was so modular - every manufacturer rolled their own combo of CPU/GPU/DRAM/Flash/whatever which allowed for a very cost efficient solution for the particular task. Intel doesn't do that yet, they are currently only in the phase of pushing the GPU in, but a modern ARM chip is really a SYSTEM on a chip, so when you compare wattage and cost with an OMAP3 it is a total of north+southbridge+DRAM+FLASH+video stuff+etc.

Second, Intel needs to address idle consumption. Again, this is something historical, the original PC design (as that's actually what people actually mean with X86) was never meant to really be idle, and the hacks/tricks to save energy are just that - hacks and tricks as they had to preserve a good deal of backward compatibility. This is also the (hardware part of) the reason why a N810 can spend more time idling AWAKE than most notebooks in stand-by mode. X86 *can* be made more efficient, but at the cost of losing compatibility. But if you lose that, what is the point of X86 in the first place ?

Third, the ARM core is, even after decades of improvement, pretty small and this reflects well on die sizes. Due to historical baggage, this cannot be said about the X86, it's huge compared to an ARM chip (plus, the reliance on bigger L1/2 caches and long(er) pipes does not help). So while the benchmarks look good for Atoms, ARM based solutions are still pretty much ahead when it comes to performance/watt (or even performance/cost). You're basically sticking a revamped truck engine in a sportscar and hoping the brute HP will pull you through. This sounds pretty much like a Dodge Viper, cool in demos, but keep near gas stations and a healthy reserve on your credit card