What percentage of America is literate?

According to the CIA World Fact Book, based on data from 2003, defined as people over the age of 15 who can both read and write, literacy in the United States is at 99%, with both 99% of men and women meeting the CIA definition of literate.

There is wide scale belief that this figure is in decline, and that a significant number (not a majority by any means) of American citizens operate barely at this level of defined literacy.