I rode bikes for the longest time and I would say 60% of bikers acknowledge 'the wave' when passing each other in opposite directions... 30% actually instigate the wave and the other 10% couldn't care less to acknowledge the comradery that's shared amongst the passion of biking.
Isn't that what it's all about... When someone on the street walks by and says 'Hi" most people would respond 'Hi' back (I'm saying most) but I grew up in a small town where if you didnt reply back - you were looked upon as being rude. Now if someone waves to you that obviously shares interest in the same passion as you, wouldnt it be polite to wave back...
I was out for a ride on a back road last week and while sitting at a stop sign waiting to turn right, an elderly couple approached from the left in a silver 986 and they both gave a great big wave as the passed by; As I waved in return, I thought to myself, hey they obviously share the same passion and think the same in return... kind of makes you feel like good about owning one of these great cars :-)
Dont be lazy and lift your arm.... pretend your toasting with a beer in one hand...