I have a uno3 and the uno2.
Here the deal I uploaded the ArduinoNunchuk example code in the Uno2 and it doesn't work it's like the SDA and SCL are not hooked up.
So pull out the Uno3 and and load the same code and it works fine.
So is not the SDA SCL lines in the same place on both I found this
Revision 3 of the board has the following new features:
1.0 pinout: added SDA and SCL pins that are near to the AREF pin and two other new pins placed near to the RESET pin, the IOREF that allow the shields to adapt to the voltage provided from the board. In future, shields will be compatible with both the board that uses the AVR, which operates with 5V and with the Arduino Due that operates with 3.3V. The second one is a not connected pin, that is reserved for future purposes.