Do you attempt to explain or simplify proxy/other error messages for users?
For the umpteenth time someone has come in and said "can you unblock $foo".
"er...we're not blocking $foo, what message do you get?"
"That's nothing to do with us (a)their webserver is broken, b) you're typing in the wrong url, c) that page doesn't exist)".
I mean, I've customised the Squid error pages to include information in plain English and the "blocked" vs "site is broken" notices are different - one is colourful with images, the other is not. But every time a webserver gives them a 404 they think it's our filtering.
*wanders off to see if anyone makes posters explaining webserver errors*