Except for one heretic (who uses Slackware) we all use Debian ever since said heretic introduced it to the institute in the mid-1990s (he switched later, God knows why...). We have 5 servers, 29 workstations, and 3 notebooks with Debian.
The software is mostly scientifically relevant stuff like LaTeX, C++, some graphic tools like xfig, standard apache and e-mail/internet stuff and things that help to scan and burn.
Why we run Debian: Very convenient upgrading mechanism, security issues, rarely need the latest drivers for fancy hardware anyway (so no drawback in using Debian), installation via net (local mirror) straightforward - well, and of course additionally all the standard reasons why Linux over Windows, but that is not Debian specific.