David Mehegan points out this report from Bowker, which projects that "U.S. title output in 2007 increased slightly to 276,649 new titles and editions, up from the 274,416 that were published in 2006." If print-on-demand books are factored in, the total number of 2007 titles is 411,422 (the Bowker report calls the rising number of new p-o-d books "staggering", but they are careful to note that they'll be tracking trends in this area carefully "in order to get a sense of whether this is a sustainable trend or a one-year spike.") Prior to this year, p-o-d titles have been included in the overall statistics; from now on they will be measured separately.
"The big winners last year were once again Fiction and Literature. There were 50,071 new fiction titles introduced in the U.S. last year, up 17% from 2006, and the number of new titles in the category in 2007 was almost twice what it was as recently as 2002. Similarly, there was an 19% rise in new literature books last year, to 9,796, which followed a 31% increase in new literature titles in 2006. ... [J]uvenile title output, which makes up more than one out of every 10 new books introduced into the U.S. market, was down again slightly last year and has now seen steady erosion in each of the last three years since its Harry Potter-influenced peak in 2004."
"The number of new business titles fell to 7,651 in 2007, down 12% from 2006, and the number of new sociology/economics books dropped to 24,596, an 11% decline from the prior year. ... [T]here were also slight dips in the Religion (down 5% in 2007) and History (down 3%) categories, both of which had experienced double-digit increases in 2006.
I'd be interested to see breakdowns within the print-on-demand category; the report simply describes these titles as "reprints of public domain titles and other short-run books." My guess is that these are mostly fiction as well, but some data on that might be enlightening. Also, I can't say I'm particularly surprised at the downticks in those particular non-fiction categories: business, sociology, and economics texts seems good candidates for non-traditional publishing methods, and after the large increases for history and religion in '06 a slight correction was probably in order.
But overall, as Mehegan points out, "Kindle has a long way to go to put the printed book out of business." The state of the codex is strong.