Everybody and their brother usually waves down here in Georgia. Granted this is the south and we're friendly folk! Toss us on motorcycles and we've got our own private club and an excuse to wave at anything on two wheels.
There's only been a few instances where I haven't been given a return wave and I figure it was because I wasn't seen due to the traffic congestion. On the way home from work today, I saw about 7 people out on their bikes. 7/7 for waves. Everything from a Goldwing, a cruiser type, and few sporties. I had some dude on a sports bike (didn't catch what type it was) come up in the fast lane on the two lane highway we have that runs around the city. He beeped his horn twice and went flying past with his left arm raised up. Of course, I saw him approaching from way back and was making sure he caught up to me before I got off on my exit.

I waved as he was starting to pass me. I'm going to file that use of the horn for the next time I pass a biker. It's about all it's good for, lol.