Its just a smaller production size, so the chip can run cooler, since the lower you go, the less voltage you need to power it, and also the cheaper it is to manufacturer (being able to put more CPU's on one piece of silicon at a time)
The lower you go though, the more chance you have of electrons starting to jump, causing well... a none working computer part.
They have figured ways around this though, so expect in the next few years 30nm ones, etc.