I'm sysadmin at a college. All our web traffic used to go through this big expensive Solaris box that used commercial content filtering software to protect the student kiddies from sites they shouldn't look at. Lots of people were always complaining to me that the students were looking at sites they shouldn't be allowed to look at, and lots of other people complained that they were banned from sites which had nothing wrong with them.

One day the hard disk on this proxy server died so as a temporary solution I pulled out an old pentium75 and put linux on it and downloaded a perl script which did web proxying. Management immediately complained that there was now no content filtering so I added a bit of code to the proxy script which went something like:

if ($buffer =~ /naughty_word|another_naughty_word|XXX Sex/)
$buffer = "You're not allowed to look at this web page!";

It worked great. I now get less complaints from the people who thought our filtering was too liberal and from those who thought it was too restrictive than I ever did when running the expensive and sophisticated commercial filtering software. The p75 linux box with its perl script has stayed right where I left it ever since.