As someone who takes photos, I'd say getting a wave, thumbs up, etc, is few and far between, so I don't expect it. I always acknowledge if a driver has slowed down, paused, or gave me a wave though. Perhaps some of that is on my part though, as I tend to keep myself to myself, whereas I know others make a point to get to know other enthusiasts, drivers and so on, so they're more likely to see a familiar face in that respect. 

On the other hand, other than speeding up/covering face, it's pleasing to say that I've had very few incidents with drivers when I'm photographing the bus. I've had a handful of incidents up here; verbally challenged twice, and a couple of finger salutes. The worst run in I had was in London, where a driver took so much of an exception with me that he got out of his cab and off his bus. This one escalated to the point of asking a friend to grab a hold of my camera for a minute, as I stormed over to have a 'quiet word' with the driver. Perhaps not the reaction he was expecting, he sharp got back in his cab and closed the doors mind...

Oh and I did have some pratt from Nexus try and tell me that photography was illegal once at Heworth.