Baldwin Linguas is a small language services agency, providing translation, interpreting, and localization services and multi-lingual web design and mastery.
We have used GNU/Linux since inception, having used Fedora, PCLinuxOS and Ubuntu, and even rolling our own (LinguasOS, based on PCLinuxOS) for a while, but finally joined the Mothership around early 2009, and haven't looked back since.
Unlike other distros, Debian Stable seems to never break stuff. It lives up to its name, so we can focus on our translation work, rather than waste time fixing stuff. Heck, even in the upgrade from Lenny to Stable, Debian just worked. Took a couple of hours to apt-get the upgrade, and B00M, we were back to work, seemlessly. Amazing! (especially cool that Squeeze was released on my birthday!)
We use Debian on all desktop computers in-house, and our 1 in-house server (in-house server mostly used for file server over ftp, ssh, and a Pootle installation, plus internal dokuwiki. Our main website is hosted off-premises on a CentOS server, sadly). Our most used applications are OmegaT (this one we install from the project, itself, since Debian's version is old), OpenOffice.org, for translation work, Vim and Iceweasel (online research, communications) for web services work. I (owner) use Mutt for e-mail. We use GIMP for creation and manipulation of graphics for web services work and marketing materials. Many gnu and bash tools see regular use, with a lot of scripting to automate much of the manipulation of textual materials (especially sed, awk, perl). Everything, really, is on our Debian machines, including all the boring, back-office admin stuff, all webdev tools, all translation tools, all word processing, everything.
If I had to try and use Windows for this stuff, I'd probably shoot myself.