YouTube has announced on it's official blog that they have launched their own URL shortening service "Youtu.be". This has been done they said to make you feel rest assured that when your clicking a youtu.be link you are indeed click on a YouTube video. Also because the link contains the video link. Developers can do interesting things with it like, show you thumbnails, embed the video directly or track how the video is spreading.
In order to use the feature you would need to use AutoShare.
AutoShare allows you to automatically share your YouTube Activity Feed to Facebook, Twitter and Google Reader. By opting into AutoShare, when you perform certain actions (specified in your Activity Feed) on YouTube, AutoShare sends an update to your friends on Facebook, a tweet on Twitter, and notification in Google Reader about those actions.
To use youtu.be manually, simply take a URL like http://www.youtube.com/watch?v=FdeioVndUhs and replace the"http://www.youtube.com/watch?v=" with "http://youtu.be/" to get: http://youtu.be/FdeioVndUhs Plug that shorter URL into a browser, and you'll see it redirects to that video.