Nano’s got the breadboard-ability of the Boarduino and the Mini+USB with a smaller footprint than either, so users have more breadboard space. It’s got a pin layout that works well with the Mini or the Basic Stamp (TX, RX, ATN, GND on one top, power and ground on the other).

This new version 3.0 comes with ATMEGA328 which offers more programming and data memory space. It is two layers. That makes it easier to hack and more affordable.

You end up paying less with Nano than Mini and USB combined.