Silverthorne's package is a miniscule 14x13mm2, and Intel claims that the device has a TDP of 2 watts at 2GHz on 1.0V. At lower speeds, the device gets down to 0.5 watts, but it's not clear how far down Intel will have to ratchet the clockspeed to get there.
Intel has equipped Silverthorne with a new low-power state, called C6. When Silverthorne is in C6, the only components that it leaves turned on are the SRAM that saves the existing processor state and some circuitry that can wake up the processor again when it's needed. (Getting out of C6 takes about 100 microseconds.) Intel claims that their testing indicates that Silverthorne can spend as much as 90 percent of its time in C6; if that's true, then that will bring the chip's average power dissipation far below its stated TDP.
Having tried a few of Intel's Silverthorne-based prototypes, I must say that I wasn't particularly impressed. I own a Nokia N800 and an iPhone, both of which are ARM-based and both of which give a nearly complete Internet experience in a smaller form factor than Silverthorne will ever fit into. Indeed, at one point during a sit-down with Intel the rep told me that the warm, bulky prototype I was holding would give me the "full Internet in your pocket." I started chuckling, pulled out my iPhone, and said, "I already have that."