SRON uses Linux extensively throughout the organization, running web servers, file servers, and (scientific-) desktops.
We've consolidated on Debian GNU/Linux for its stability, ease of administration, slow release cycle and overall software compatibility. Apart from the technical reasoning, there is also the political and structural: Debian is non-profit and non-commercial. It cannot be bought or sold and therefore we expect it to stay around for a long time to come.
We have about 120 Linux workstations, running Debian Jessie 64-bit, and some old 32-bit machines also running Debian. Serverside, we have about 20 running Linux, of which 15 Debian.