While their numbers are growing, Neilsen//NetRatings says African-American Internet use still trails other ethnic groups by a significant degree. Meanwhile, Arbitron and Edison say African-Americans have achieved virtual parity with white Americans when you include school and library use.
Since N//NR’s ratings methodology measures at-home (and guesses at-work) use, they are almost certainly undercounting African- and Hispanic-American use of the Internet.