If you're a parent who wants to show your child's footy skills without exposing their faces or just want to post videos of your buddies doing quasi-legal shenanigans YouTube now offers to automatically blur faces.
All you need to do to blur faces in your videos is click on your YouTube user ID in the upper right corner and select the link for the Video Manager. Find the video you wish to alter and click on the Edit button for that video and then the Enhancements tab; you'll see standard editing options such as image stabilisation and trimming the video length, but if you click on Addition Features under the video preview you'll see the option to blur faces.
The blurring isn't perfect; if the subject turns their face away from the camera or if the camerra tilts sideways the blurring disappears, so if anonymity is mission critical you may still need to break out a video editor. Keep in mind that there's no going back to the original non-blurred faces video so make sure if you do this to save it as a copy on YouTube itself or offline.
Face blurring: when footage requires anonymity [The Official YouTube Blog]