With the exception of new age, the smallest genre tracked by Nielsen SoundScan, R&B and rap suffered the biggest declines in 2006 of all styles of music.

R&B, with album scans of 117 million units, was down 18.4% from 2005, while the rap subgenre's 59.5 million scans were down 20.7%.... Since 2000.. R&B is down 41.4% and rap down 44.4%. [see full story for more it includes some interesting guesses for the decline including the RIAA standby of piracy but really don't address the Hip-Pop problem plaguing rap that is similar to the hair metal craze of the late 80s and emo now= lack of innovation. If you already own the original why would you buy an inferior copy or rehash?] - more on this story