I wave and nod "thanks" to motorists who, say, allow me to access the left turn lane, or other acts of kindness. If it's something that I'm entitled to by rights, then no, I do not wave. But, "random acts of kindness" do occur, and I acknowledge them, whether I'm in my truck, or on a bike.

On yesterdays ride, I was in the right hand lane, coming to an intersection. The motorist that was right behind me was turning right, and I was going straight. Since there was very little traffic so early on a Saturday morning, I moved over and gave him the lane so he could turn right, while I waited for the signal to turn and continue on. He gave ME a wave and nod of "thanks".