This from a PR rep:
In 2011, the most recent numbers available, there were 347,178 printed books published in the United States. That was up 6 percent from the previous year, according to Bowker, which provides book industry statistics and trends.
For those of you in the book-planning phase, it may be helpful to know which categories saw an increase in publications. They were education, up 20 percent; music, and psychology and philosophy, both up 14 percent; religion, up 12 percent; juvenile, biographies, and business, all up 11 percent; and fiction, up 13 percent.
Those are just the numbers for printed books. E-books are harder to gauge, but they’re a large and growing share of the market. For those I could find only sales numbers. For 2011 they were $1.1 billion to $1.97 billion, according to two different counts.