Teresa at Making Light has a great post about how deaf people are using YouTube:
Why did it not occur to me that the signing deaf would be using YouTube as a public forum? This is transformational. Many of them aren’t comfortably fluent in written language. For many more, sign is and always will be their first language. YouTube gives them an easy, expressive, unmediated channel for many-to-many communication.
Via MeFi, which has some more discussion.