As soon as I see another rider, I'll jump up and stand on the seat and wave with both arms.
Nah, I'm usually concentrating too much on the road to notice other riders.
I'll usually nod when I see another rider wave at me, though. I've never liked taking my hands off the controls while at the same time taking my eyes off the road.
The first time I waved to a biker on the Busa I just about shid my pants and dislocated that shoulder