I wrote my first book almost 15 years ago using MS Word on a Mac Plus. I wrote additional two books with Word, and managed to finish my Masters thesis with Word, despite big difficulties. I had to rewrite a lot of equations and make numerous changes to the typography to make the thesis readable. After that I switched over to LaTeX. Of course, for shorter pieces I'm still using Word, among other tools. But Emacs, LaTeX and the Unix tools are a powerful combination. And now I have on my iBook running Mac OS X exactly the same TeX system as on the Linux, Compaq Alpha, and SGI systems at work. Basically all (several dozen) books published by my employer are typeset using a LaTeX style designed mainly by me.