I do a lot of technical writing both because I enjoy communicating and to earn money. Recently, the AI project that I am working as architect and lead AI developer passed a performance milestone so we get more people and resources. As a result, I find myself writing more architectural documentation and doing less Lisp programming - so it goes :-)
As a computer scientist, I spend a reasonable amount of time tweaking my software development and technical writing work environments. For software development, I almost always prefer a fast Linux box with just the tools I need - no fluff to act as a distraction.
Unfortunately, my favorite writing environment is heavily Mac OS X dependent, largely because of the OmniGraffle technical drawing tool (I am addicted to using it and I highly recommend it.) So I am stuck on a Mac for writing most of the time. I also strongly prefer Latex over Microsoft Word or OpenOffice.org for writing (much more efficient use of my time!) While I am very happy using Emacs+autex for Latex work, there is something a little better: the free TeXShop Latex working environment for OS X.