I use LaTeX for almost all my stuff I create.

It's good for any letters (manual and automated created), posters, music notes, good presentations, books (can handle thousands of pages perfectly) and much more.

The letters look perfectly, much better than OpernOffice or so. It is a Text SETTING SYSTEM, not only a pdf-creator.

Try out.

been using TeX (plain mostly, occasionnally LaTeX) for years for all
kinds of stuff: writing letters, resumes, math articles,
documentation, goofy stuff... You can even write music scores,
guitar tablatures, crossword puzzles... It's so flexible.

All you need really (aside from the compiler) is a text editor.

You can even do everything from the CLI, without bothering to open
an X session. I do that quite often.
There are a number of framebuffer tools that can display the output (pics, pdf ...)

I'm a graduate student (doing an M.S. in Mathematics) and I use LaTeX for writing papers, as well as for writing the tests, quizzes, and handouts for the classes I teach. I'll also use it for my upcoming thesis.

It's a great tool. It allows you to create really professional math documents, as well as documents for other things. It has document classes for articles, books, letters, and AMS (American Mathematical Society) articles.

I've been using LaTeX for about a year now, mostly for my lab reports in Chemistry. It's way more flexible, reliable and powerful than OpenOffice (or similar) ever was to me; I don't really see the need for keeping an office suite around anymore :). If anyone is looking for more documentation, the Tex Users Group has compiled a pretty comprehensive list here.

Some of you might also be interested in GraphViz. It is basically to diagrams what LaTeX is to documents, and it is supposed to integrate nicely in TeX through the dot2tex module. I have yet to play with it, but it is certainly on my todo-list ;)