I do a lot of math. That makes LaTeX much faster to write than any alternatives. At this point, in math classes, I can take notes in real time. A properly written LaTeX file is also much faster to modify -- if I'm giving a presentation, and I have an arrow between two equations on different lines, when I rearrange things, that arrow keeps pointing between those two things. I can generate LaTeX programmaticly (e.g. tables of results). I can keep it in version control and have sensible differences between versions.

My major problem is that it does not handle animation and video well. Those are increasingly coming to be critical parts of presentations, and are the major thing pushing me towards OO.Presentation or PowerPoint or similar.