Arduino Nano is a surface mount breadboard embedded version with integrated USB. It is small, complete, and breadboard friendly. It has everything that Diecimila/Duemilanove has (electrically) with more analog input pins and onboard +5V AREF jumper. Physically, it's missing power jack, so it works with a Mini-B USB cable instead of a standard one. The Nano will automatically sense and switch to the higher potential source of power, so there is no need for the power select jumper.
The Nano has the breadboard-ability of the Boarduino and the Mini+USB with smaller footprint than either, so users have more breadboard space. It has 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, making it easier to hack and more affordable.
Automatic reset during program download
Power OK green LED
Green (TX), red (RX) and orange (L) LED
Auto sensing/switching power input
Small mini-B USB port for programming and serial monitor