The remarkable transformation of the music industry from 1980-2010 is brilliantly illustrated in a 30-sec animated graphic sequence of pie charts. You can examine each frame individually. Based on US data. Dramatic and thought-provoking.
See: Digital Music News
Here’s another way of looking at it. Shows the recorded music industry peaked in 2000.
The image comes from a report discussing the transition of literature from books to digital format (pdf).
I found this in a great post on the the FGV Guitar blog which investigates whether declining music sales are affecting the guitar. Much of popular music features few recognisable guitar parts.