This post by Narayan Newton didn't make it into my aggregated High Availability/Performance categories in my Reader, but I picked this up from Dries on Twitter and though it's light on details, is an interesting read.

Drupal.org now with caching

We've got a prominent client with a very high-traffic, high-load website that is predominantly PHP, PostgreSQL backend, MVC design (uses Smarty for compiling templates etc etc).

Previously the site ran rather hot on an old physical server that had plenty of guts behind it. However recently this client's website has been migrated to virtual infrastructure in order to decommission the old physical server.