The ability to have the Uno show up as a keyboard, mouse, joystick, etc.
2013 New Version
This is the new MEGA2560 R3. In addition to all the features of the previous board, the MEGA now uses an ATMega16U2 instead of the ATMega8U2 chip. This allows for faster transfer rates and more memory. The MEGA2560 R3 works with all existing shields but can adapt to new shields which use these additional pins.
•Microcontroller: ATmega2560 •Operating Voltage: 5V •Input Voltage (recommended): 7-12V •Input Voltage (limits): 6-20V •Digital I/O Pins: 54 (of which 15 provide PWM output) •Analog Input Pins: 16 •DC Current per I/O Pin: 40 mA •DC Current for 3.3V Pin: 50 mA •Flash Memory: 256 KB •SRAM: 8 KB •EEPROM: 4 KB •Clock Speed: 16 MHz