Harold Underdown has done some interesting digging into the statistics about YA publishing that were used by journalist D.B. Grady for an article in the Atlantic. But whether there were 30,000 YA novels published in 2009 (unlikely, as Harold demonstrates) or 8,000 (as Harold estimates), can we all agree that there are too many? My own recent research into this question revealed that while the number of hardcover books published for children and teens in 2010 (about 4500) was just 25% higher than the number published in 1998, the percentage of those books that were novels almost doubled, from 18% to 33%. (I did not differentiate middle-grade and YA, but I'll try to recrunch and get back to you.)
On a related note, have you ever noticed how much the menfolk of the children's book biz love to count things? Ask Peter Sieruta or Jonathan Hunt or Ray Barber about what-won-what-when-and-how-many-times and prepare to be amazed. Maybe Travis Jonker should design some Newbery-Caldecott trading cards, complete with stats on the backs.