US album sales have fallen 55% since 2001

"Since peak year 2000, US-based album sales have dropped an unbelievable 514.6 million units, or 54.6 percent. In 2000, the climax of a dreamlike 90s, album sales surpassed 943 million units, according to figures published by Nielsen Soundscan."
Source: Nielsen Soundscan, quoted by DigitalMusicNews 27th January 2009