I have begun developing a Lego Power Functions IR library for Arduino. Yeah, I know that there exists at least one already (Arduino-PowerFunctions). But I have only found libraries that can send commands, not receive. My main focus in the beginning for this library is receiving Lego Power Functions infrared commands, not sending.
I have tested the library on an Arduino Uno (Atmel ATmega328P) and an Atmel ATtiny85 (if your interested in a Lego Power Functions IR receiver run by an ATtiny, then take a look at this dutch guys project – and when you visit his site, make sure to also read his opinion on Arduino).
It’s still beta (or should we call it alpha), but if you are interested you can download the source code.