BioDec is an Italian company specialized in bioinformatics. We run Debian on almost all of our servers: We use it for both infrastructure, like e-mail, web services, firewall, etcetera, and for bioinformatics clusters (which is one of our business).
We have slightly less than 20 Debian servers (both virtualized and physical) in our offices and manage less than a hundred of them (both virtualized and physical) for some customers of ours.
We chose Debian for the support from the Debian people, which is simply the
best around. From time to time we complain about missing features and
strange quirks, but overall we chose Debian because it has the best
hacker team ever. Go on Debian, and fly high!