How do I watch Youtube videos without Flash on Safari?

There should be a preference thing on YouTube to select HTML5, but they've reorganized the page so many times since I last tracked it down that I have no idea where it is now.

Instead, I have ClickToFlash installed (it's under "Most Popular" in the Safari Extensions Gallery); open its preferences (Safari Preferences... > Extensions) and you can tell it to always use HTML5 for YouTube and other sites that support HTML5 in place of Flash.

Yes, most YouTube videos are also available as HTML5 videos. You need to sign in to YouTube and join the HTML5 trial -- see http://www.youtube.com/html5 for details.

I use the FlashToHTML5 Extension, works great!

FlashToHTML5 replaces the CPU and memory hogging YouTube Flash Player with a HTML5 player. Not only will it look nicer, you will also notice that your computer will run cooler and faster. If you use a laptop, you will also notice that the battery life of a fully charged battery will increase.