In comparison there were just under a billion units sold in 1999 and the backstreet boys had the biggest album with over 16 million copies. Last year the top seller, Lil Wayne only sold 2.8 million. It took the b-boys just over a week for comparable sales at the peak of the market.
If I'm not mistaken, Norah Jones first album was the last to break the 10 million barrier.
Total units sold started dropping at an annual compounded rate of 6%/year in 1999 through 2004. With the introduction of iTunes in 2003, "album substitution" started to take hold and the decline accelerated. Albums were being replaced by single track downloads on iTunes at a rate of roughly 1.4 downloaded tracks per CD album. With an average of 12 tracks per cd.. that's an 88% drop in per unit sales (1.4 tracks are around $1 on iTunes vs. $16-$20 for the CD album).
The music industry is alive and well but the record industry has basically been obliterated.