Here's a video of someone playing Mario Kart: -
https://www.youtube.com/watch?v=_zPm3SSj6W8" onclick="window.open(this.href);return false;
Switch to 1080p and it'll switch into 60 FPS mode. It only works on Chrome, IE and Safari (I think) at the moment. It's not working in Firefox.
EDIT - Oh, and make sure you're using the HTML5 player. You can opt in here: -
https://www.youtube.com/html5" onclick="window.open(this.href);return false;
YouTube offering a 60FPS option for some videos
Moderator: Sigma