Intel Medfield idles at 2.6 Watts and peaks at 3.7 Watts. The Windows 8 tablets will be using its successor, Clover Trail. there are roughly 40 tablets that will launch with it.

Intel isn't efficient enough for phones (see the comment below about the 1W tdp ARM SoCs) but they are efficient enough for tablets. Every report indicates they are price competitive as well.

Additionally, Clover Trail is being printed at 32nm vs. Krait's 28nm. It was just announced that Intel is going to bump up their timeline and move their Atom SoCs to 22nm next year.

It's not like Intel is destroying ARM by any means. They are barely keeping up. But that's HUGE on Windows where you have decades of legacy x86 apps that you might want to run.