STC Accessibility Blog: What’s Unclear about Captioning?
This is an article worth mention for a number of links provided in it.

FCC Facts about captioning -
Background of captioning, rules and exceptions, how to file a complaint, and:

Benefits of Closed Captioning
Closed captioning provides a critical link to news, entertainment, and information for individuals who are deaf or hard-of-hearing. For individuals whose native language is not English, English language captions improve comprehension and fluency. Captions also help improve literacy skills. You can turn on closed captions through your remote control or on-screen menu. The FCC does not regulate captioning of home videos, DVDs, or video games.

Twitter list on captioning (and stcaccess has many other lists I’d follow if I had more time to read)

Who is required to Close Caption?

-With only a few exceptions, all programming for broadcast in the United States must be closed captioned.
-Federal Agency training videos (Section508)
-H.R. 3101 was introduced in June 2009 by Edward Markey (D-MA). Called the “Twenty-First Century Communications and Video Accessibility Act of 2009,” this legislation will, if enacted, amend the nation’s Communications Act.