Institute for Learning and Research Technology, University of Bristol, UK

We have around 100 Debian based physical servers and Virtual Machines running on Xen using Ganeti cluster manager, Bcfg2 configuration management system and agile/CI deployment methodologies. The services range from Web Content Management Systems for UK Higher/Further Education Institutions and bodies, to a large UK Academic Survey Tool, to JISC funded research and development projects such as semantic web and mobile web technologies.

We use Debian because it's reliable and stable over long service life cycles whilst allowing us to rapidly deploy Open Source Software based environments.