You've got pins 4 and 8 reversed. Pin 4 is ground and pin 8 is VCC. Also, all your LED's are reversed.--The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons
If you've only got a 55mAh battery the shunt regulator you're building will be pretty wasteful. I'd go with a 3.3V regulator if you really want 3.3V (any reason you don't want 5V?) You can get a standard 3.3V regulator (LM1117 and others) or try to find one with lower operating current to get a bit more battery life.--The Flexible MIDI Shield: MIDI IN/OUT, stacking headers, your choice of I/O pins
How about some resistors to limit the base current ?Don
Small surface-mount package or small through-hole package?
Going from 12V to 3V3 means that the regulator has to burn a lot of power. Therefore it will get hot. Make sure you don't exceed the power rating of your regulator. You can be within the current ratings but exceed the power ratings very easily on most devices.See:-http://www.thebox.myzen.co.uk/Tutorial/Power.html
Mike is not talking about current. He's talking about what happens when a regulator must make the voltage difference between 12 and 3.3 "go away". It becomes HEAT.