Microsoft Research uses Kinect to translate between spoken and sign languages
This would be a good application for google glass (would only work one way). Other than that, I see no benefit over a simple pencil and paper for face to face communication, or a simple text chat for anything other than face to face. Although I will say that I have had text chats with deaf people before, and the text was definitely based off sign language (at times it was difficult to understand because the grammar is so different).