There is no doubt that YouTube has some pretty strange stuff. At times, very inappropriate for a classroom or any educational setting. However, there is plenty of very good, educationally sound material on YouTube as well. There are a number of reputable news outlets that utilize YouTube for posting their stories. Additionally, as we enter the mid-term election cycle, there will be a bevy of political content available as well (which could be good or bad!).
A member in the Verizon Thinkfinity Community suggested a website that will allow the user to enter the URL to a YouTube video and it will return a substitute URL (kind of like Tiny URL if you know how that works) that you can set a link to, email to yourself (or others), post to your blog (or other social networking site) and display the video without ANY of the ads or alternative content or suggestions.
It is called "Safeshare" - I've tried it and it seems to work quite well. I was able to paste the URL of a YouTube video into the box and voila' I had a new URL that opened in my browser and played the YouTube video without any of the extras - that can often be a deterrent to showing the videos in a classroom. Here is an example.
I have not tried this behind a firewall that blocks YouTube, so I don't know if it will bypass a filter. I am NOT an advocate of bypassing a filter anyway. However, if your school does allow YouTube, this is still a very useful utility to prevent any questionable content from accidentally being displayed when you want to use a YouTube video in your classroom, or, perhaps include it in a distance learning environment.