Any users on our campus who were proxied/filtered got lovely "Page cannot be displayed" messages. So, tried power cycling equipment, the proxy server, opened tickets with our ISP, and our proxy server provider. All systems nominal to everyone, but still, no internet access anywhere. There were a couple of NAT table anomalies but nothing serious, and Tampa (where the company that provides the filtering) had a bit of a problem getting into the proxy server itself.
Well, after going 'round and 'round, with everyone saying everything should be working, one of the people from Tampa sees something. Apparently, all the logs on the proxy server were causing the machine to choke. He cleared out the logs, and set up a job to do that automatically, then rebooted the system.
Voila! NOW, all systems nominal.
Off to get a haircut, and have a weekend off.