Holy shocking question batman!
Yes, I thank my instructors daily. I pay for instruction in Aikido technique, but my thanks comes as recognition that they teach me much more than simple moves. When they help me make connections, give me positive reinforcement, or just give me their time in discussion of Aikido they are giving me gifts beyond what is expected. I also try to thank them by training as best as possible. It's amazing what kind of power looking someone in the eyes and thanking them sincerely has. As a teacher by profession (not Aikido), I know that I do not expect thanks for doing my job, but when it happens sincerely it recharges my energy and it makes me want to do even more because I know the energy that I put forth is being used and not wasted.
Someone gives you the gift of Aikido and you don't thank him???
Most shameful indeed. But then, I've only ever had good instructors.