Hooray! I delete all cookies on session end and I don't have flash installed. Having to remember to go to youtube.com/html5 every time I start a new session has been frustrating.
Also, the HTML5 player has a nice feature to change the rate at which the video plays, which makes watching long talks a lot easier.
I much prefer to have the option exposed in the UI, but you can do this with any HTML5 video element by setting the video element's playbackRate. Often, it's as easy as 'document.getElementsByTagName('video')[0].playbackRate = 1.5'. I have a bookmarklet that does exactly this, so I love to see HTML5 video being the default more and more.
Also, the HTML5 player has a nice feature to change the rate at which the video plays, which makes watching long talks a lot easier.