The Register website and infrastructure use a variety of open source products, including Apache, MySQL, PostgreSQL and Perl all running on Debian GNU/Linux. As of this writing in Nov 2011, all of our public facing services along with many of our internal and development machines are running Debian (or Debian based distributions like Ubuntu) and we see nothing else that comes close to the quality and utility of the Debian OS.
Debian provides a solid platform for our DNS, email (including a mailing list for Reg readers), the dynamic and static parts of our website and production toolchain, supporting millions of our readers each month.
We were particularly attracted by Debian's reliability, stability, and flexibility, but most of all by its unmatched support for remote administration: since the system administrators and the systems themselves are separated by several hundred kilometers, it's especially important that as many tasks as possible can be accomplished remotely. Apt makes remote package management and upgrading trivial, and the Debian organization's enlightened and rapid response to security vulnerabilities lets us sleep easy in our beds.