I am a mathematician, tutor and programmer.
I use TeX a lot. I am not keen on LaTeX, though. For my degree paper I used plain TeX with eplain and defined what I needed.
I have used LaTeX in the past, but it was rather difficult to customize it. It involved rummaging through
.sty files and even through
latex.tex. Often I found it easier to reinvent certain mechanisms (and bypassing LaTeX's ones) so they worked the way I wanted them to, resorting to primitives and plain TeX commands. Certain mechanisms were useful though, so I've put up with it. The discovery of eplain changed it all. In fact, it was just what I was looking for, and planning to write myself before I knew it existed already.