robitabu:
retrolefty:
...just enable the internal pull-up resistors for those pin you will not be using...I've read Atmel's datasheet in the meanwhile (why don't I do that before starting a new thread?!!). It clearly suggests enabling those internal pull-ups instead of wiring the free pins to Vcc/GND. I'm glad to see Lefty's suggestions keep proving themselves rock solid
I will definetely enable the pull-up resistors and not ground anything at all!
Be careful and judicious with your praise. I think you find anyone around here with a high post count has contributed their fair amount of brain farts to go along with their useful tips. 
Lefty