Windows 8 Developer Preview was made available last week and it came with Internet Explorer 10. Internet Explorer 10 can be started within the Metro UI and also in the desktop mode.
However, when started in the Metro UI, Adobe Flash plugin is unavailable and hence you cannot play YouTube videos. There is a workaround for this as Internet Explorer supports the next generation HTML5 capabilities.
YouTube now offers an HTML5 trial on their website. All you need to do is to activate the HTML5 trial using your YouTube account. To activate HTML5 trial, go to www.youtube.com/html5 .
Once you opt-in for HTML5 on YouTube, you can start watching YouTube videos on IE10 in Metro mode.