Safari, the Apple browser (that works on both pc and mac) updated to version 5.1 this week. This update included the ability to add extensions, similar to what you have been able to do with Firefox for several years.
For teachers the extension ‘A Cleaner YouTube’ is a no brainer, it removes everything off the YouTube page apart from the video you want to watch. You can install the extension here.
So, if you want to use YouTube in the classroom and you have been put off by the related videos or comments then install Safari and add the extension for a clean view of YouTube.