YouTube has launched their own URL shortener. This URL shortener is exclusively for YouTube videos which means that you know which site you are going to.
"To see this feature in action, use AutoShare to link up your YouTube account to social networks like Twitter and Google Reader. Then, whenever you favorite a video on YouTube, for example, that action will get syndicated out to your network, who will see this shortened edition of the video's URL.
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."