Next week Intel will show off a new line of Haswell-based ultra-power-efficient processors at its Intel Developer Forum in San Francisco. CNET writes Haswell will be much more energy efficient than the current Ivy Bridge processors, the site says the lowest-power Haswell chip will have a TDP of just 10W, significantly less than today's 17W. The lower power consumption will make these chips much more attractive for tablets and other compact devices. It's still nowhere near close to the power consumption of ARM-based chips though, these processors are typically rated at below 2W.
And that's one of the reasons that Microsoft chose to come out with two version of its Surface tablet. The first Surface products will run an RT version of Windows 8 designed for power-efficient ARM chips. Later Surface products will have more powerful Intel Ivy Bridge processors that run the full Windows 8 Pro version.
Intel continues to offer its Atom series of processors that are rated as low as 2 watts, but they haven't been popular as Intel had hoped because of performance issues when running the full desktop versions of Windows.