Our school had tried all sorts of completely stupid stuff.
Eyeguard was the first. It took snapshots of your laptop screen (looked for stuff like porn). I don't know how good it was at detecting that, but I do know it used 40% CPU constantly. So I simply ended the process, tracked down the .exe, and renamed it. Whenever the tech guy would come to check our laptops, I'd rename it back, and reboot.
I also used Knoppix regularly, which naturally didn't use EyeGuard.
After about 95% of the school started disabling it, they stopped installing it on our PCs. It was funny, because they knew we were turning it off, but they couldn't really do anything about it.
Then they started using some web filtering system that I don't remember the name of. It was pretty damn effective. It used a proxy, and disabling the proxy in any way (Even using Knoppix) resulted in nothing. It filtered a lot of common flash gaming sites, porn sites, and such. The most annoying thing however was that it blocked large file downloads (like anything larger than 2MB).
Then we started using CGI Proxies. While it was unable to get around the file size restriction, it got around nearly everything else. Because of this, they continued to tighten the filter more and more, until...
They broke it. Literally, the web filter crashed from the amount of filtered sites. The internet was down for a couple days, but at the demand of the teachers, the internet came back up with no filtering whatsoever.
In addition to the proxy and filter, they also had port filtering. They started blocking common IM ports, like AIM's. We kept changing the ports, finally resorting to 80. They then implemented packet shaping, which killed all of it.
That also died when they brought the internet back up. There were no filtered ports, no proxy necessary (it was there but no one used it), and no web filtering.
For the last two years of my time at the HS, they never did get the filtering working properly again. That is, until the last month of my senior year.
This idea was insanely awesome, but also insanely dangerous. One kid, who assisted the librarian, had easy access to the server room, which was attached to the library. One night, he waltzed in, and plugged in a wireless AP. It had a big custom antenna, with it's power boosted quite a bit. He hid it somewhere in the server room next to one of the other wireless APs that the school had.
He plugged that wireless AP into the router that supplied internet to the servers. After an hour of configuration, he had set up a new private wireless network using the school's internet. It totally bypassed all the server's software and filtering, and was strong enough to reach about half of the school, including the cafeteria (major hanging out spot). He gave it to his friends, who also gave it to their friends.
Didn't take long before half the school was using it. I graduated, so I don't know if it is still there. I would imagine he's discovered it by now, but it was hilarious.