I can't find any clear information at all on whether it is possible to use special pins like those for serial communication and analog input for "normal" digital I/O.
For example, on http://arduino.cc/en/Reference/serial it reads:
All Arduino boards have at least one serial port (also known as a UART or USART): Serial. It communicates on digital pins 0 (RX) and 1 (TX) as well as with the computer via USB. Thus, if you use these functions, you cannot also use pins 0 and 1 for digital input or output.
That vaugely implies that maybe I can use those two pins for digital I/O if I don't need them for serial communication, if I dare to read the unwritten information between the lines.
Same goes with the analog input pins. It seems I can assign the as digital inputs, even though they are presented as analog, all I have to do is define their tasks in the sketch. It looks as if I even can make them digital outputs, in spite of the fact that they are labelled analog inputs!
But the information on alternative use of pins is hard to find, if there even is any out there(?)