I nod now that I am on a 'proper' bike (got a Fazer 600 at the start of March after passing test mid Feb). Before that I was on a YBR125 and didn't really nod (I live in london so thought other bikers would just assume I was just a city commuter).
It is nice getting nods back. Usually it is the nicer riders who do it.
One thing I have noticed is you are always garunteed to get a nod back from a blues and twos rider They never fail to.