You would never be able to tell, but Ars Techina has obtained documents (read: an e-mail sent to its employees) proclaiming iTunes as the largest music retailer in the U.S., passing even Wal-Mart. As of January 2008, iTunes now accounts for 19 percent of music sales here, to Wal-Mart's 15 percent and Best Buy's 13 percent. (AmazonMP3 is fourth.) Those numbers include online stores, too.
You may remember that Apple jumped into third place only last summer. Remember?
Some other interesting notes from the relevant NPD numbers: 48 percent of American teens didn't buy a single CD in 2007 (38 percent didn't in 2006). The last CD I bought was Above & Beyond's Tri-State when Tower Records went out of business. I think I payed $8. Also, music downloads accounted for 30 percent of all music sales in January.
In short, expect a press release from the RIAA shortly claiming that artists starve when you don't buy CDs.