You cannot kill somebody if you have a tracking device in your veins.

Medical use can be large, if the nanotech application can cure most sickness at once. Chances are it will help one one disease at a time. Think about how many cars and trucks there are in the world. I think there were about 10 million sold in the US along last year. If nanotech can be used to make a better battery (and several companies are working on it) — think about it, drive 200 miles pollution free (I know, the coal-fired power plants pollute, but it is much easier to put scrubbers on one smokestack power plant than it is to clean up the tailpipes of hundreds of thousands of cars), stop off for a bathroom break for 5 minutes while you can recharges for a buck or two.

Between medicine, materials, and information technology advances, I would say medical advances.

While it has always been the dream of life without instrumentation, nanotech can hide all the wires, switches, tests, and controls, plus a pile of redundancies inside things and out of sight. It is the ability to make diagnoses, to deliver medicines, to mend bone and tissues that will do some far more fabulous things than changing color or trapping odors or making film behave like structural steel. Good stuff ahead.

Less than 1/4 of a inch.

Clothing. The clothing will be made to change colors based on the day, or repair itself, clean itself, or even reweave itself into new shapes. Not only will clothing become more “fashionable”, but it will become safer too. If someone were to scrape a knee, the clothing might even be designed to harden as the clothing hit the surface.