PHP is supported by a number of machines provided by a number of generous sponsors. This is a basic inventory of those machines and what services they provide.
We use Nagios and Munin to monitor the machines. There is a public network status page as well as a protected area (log in with your SVN credentials) with more detailed information. The Munin web interface is available here.
Note regarding FreeBSD machines: Upgrades should be performed according to this guide.