I personally have a hearing impairment and I would prefer to be called hearing impaired. But I guess you could use the word deaf. As for capitalization it depends who you ask. Those in the deaf culture prefer to say Deaf and call their culture Deaf culture. After all, if you say someone is French or British it is capitalized. You are referring to their identity. If you just want to say someone is deaf, as in hearing loss, and without connoting a culture of signing in their own language, you could say "hard of hearing", "hearing loss", "hearing impaired", "deaf", or "oral deaf" meaning a deaf person who hears and speaks to some extent and is grounded in hearing society rather than Deaf culture.
Deaf, capitalized is politicized and I personally believe it is more fit for editorials or personal views rather than for news reporting.
Do you call black people "Black People"?
Do you call white people "White People"?
Do you call tan people "Tan People"?
For more on this topic see this article:
http://tomwillard.wordpress.com/2007/10/12/big-d-deaf-seems-big-headed-to-me/
No it shouldn't be capitalized.
It should only be capitalized if it forms part of a title.
Earth, as in we live on the planet Earth, is supposed to be capitalized. Earth, as in the dirt we walk on, is not supposed to be capitalized.
Yes, Siamese would be capitalized.
No.
No, it shouldn't be capitalized.
No it shouldn't be capitalized.
no
No, but the names of individual languages are capitalized.
no
It should only be capitalized if it forms part of a title.
Yes... indeed it is!
No, it is a common noun.
No it is a common noun.
Yes, the word "Americans" should be capitalized as it is a proper noun referring to the people of the United States of America.
No, but it is just one word: saltpeter.
No, except if the word is used at the beginning of a sentence.