What is the common use (if any) for mala beads in Zen practice. Also, is there any special etiquette involved, or other considerations?
They are essentially counting aid for concentration, you basically count them as you chant say "Amitabha", the Heart Sutra or any mantra, for example 108 times. For the technologically minded, it can be even substitute with an electronic counter.
I haven't seen beads used in any Zen sangha.