i've only been nodded at once *nobody likes me*
i try to nod to most but scooters, but im new and i have to concentrate unless im going in a straight line, and i've only ridden in winter and so passed all of 2 other bikes
if i dont nod back its only cos i dont notice or im concentrating
EDIT: i never nodded/waved as pillion unless the rider didnt acknowledge the nod cos he was busy doing something