I have been using computers for a long time (in the early 1960s my Dad got access for us to a timesharing Basic system on the Darpa Net), but I only have been using Emacs for 21 years :-) LaTeX and TeX are also old but great software, but I am fairly new to LaTex - I used it a few years ago to write the first version of my free web book Loving Lisp. The Saavy Programmer's Secret Weapon but had not used it again until this last week when I started to setup a more streamlined writing environment (more about that later).
I still think that IntelliJ is the best Java development environment, but I am trying to not do so much Java anymore - this year I have been developing mostly using Common Lisp and Ruby. Emacs is a natural fit for Lisp development, and is good for Ruby (but Ecplise+RDT is a bit better). It feels strange to still be using the same software (sort of) that I have been using for a good part of my life!
Just in the last few days, I have been finding Emacs recently to be the best environment (that I have found) for working with LaTeX - AucTeX was a 1 minute install in Ubuntu and I liked the way that it gives limited preview right in an Emacs buffer, and it takes only a few keystrokes to run LaTeX and get a real preview.
I have a good reason for getting back into into LaTeX: I love to write but I am not as enthusiastic about going with the established publishing industry anymore (I have written 14 published books, with another in progress, so "been there, done that"). I am much more enthusiastic about web publishing and alternative print on demand publishing outlets because a lot of things that interest me enough to write about are niche markets. In order to more easily write more (but much shorter) programming texts, I want to streamline and automate generating high quality text with embedded programming examples and equations. It took very little time this afternoon to set up an automated system for embedding program listings with generated output in LaTeX. Saving lots of "busy work" time lets me spend more time writing.