About the pictures, I'm proud to say that ALL of them were done in TikZ :)
My field was (or, is now) chemical reaction engineering, specifically chemical kinetics under the framework of stochastic processes. All the energy diagrams, reaction mechanisms and, in addition, automata diagrams, were available but not good enough. TikZ did a great job for all cases. I took some time to perfect them :)
So I have a fair amount of material I want to share