Well, here somebody who uses LaTeX not for mathematics nor natural sciences, but philosophy (and a lot more). LaTeX is good for formulas, yes. But to restrain it to it is like telling that you only can use a Mac for drawing.
I wrote my Magister Thesis and PhD on it. It helped me not to care nor worry about format, just about writing, and nevertheless have a visual product which gave me some extra points, I am sure. I have perfect integration of images, different languages (also old greek, sanskrit, etc), automatic stuff which Mellel claims as new (automatic format of classes, automatic generation of table of contents, glossary, tables etc, automatic generation of bibliography, internal hyperlinks in text and to outside).
LaTeX does the stuff since decades, for free, there is a huge community which makes tweaks, and you really can adapt everything to exactly the idea you have. But yes, you have to learn it. Once done, you have the power to form a perfect layout with just some minimal instructions. Lex is a LaTeX client.
How I work
Bibliography: I imported them into Bibtex(free) - used Bookpedia(payed) to scan barcodes and download all the info, but is not necessary.
Reading : used Docear (free) to integrate automatically notes (and monitor them) into mind map freeplane (free)
Writing : used WriteRoom for distraction-free writing, but there is a lot of free software out there for that.
In this moment I am evaluating TexPad - see its screenshots, you will notice it looks very like Mellel, and not because of imitating it, but because it is part of the logic of the writing-typsetting relation.
I would use Mellel as an help, to think in big documents, but as working horse LaTeX