Not all people who are hard of hearing or deaf consider themselves to be among the Deaf (upper case D). The Deaf consider themselves to be a separate language and cultural group from the dominant culture in which they live. Although the Deaf in North America use American Sign Language (ASL) as their first language, many of them can read lips and know enough some English, communicating with hearing people often presents a challenge.
A group of Massachusetts Institute of Technology (MIT) students from their Fluid Interfaces Group created a combination of hardware and software which allows people to use the movement of their hands in the air to interface with a computer. A wearable computer would allow a person who uses ASL to sign to a hearing person, and the computer would interpret the message into spoken English.
Of course an interface like that would allow many other uses too. Check out this video and short writeup from Fast Company. Amazing possibilities!