The 1,200 US publishers who supply data to the AAP reported that their collected revenues reached $2.6 billion in the first 5 months of the year, up 3.9% from $2.55 billion last year.
As you can see in the chart below, the adult segment was down 3.6%, religious presses dropped a fraction of a percent, the kid's/YA segment grew by 30.1% (don't you just love those movie inspired market fluctuations?).
In terms of formats, ebooks were one of the two bright spots in this report. The AAP says ebook sales totaled $670 million, up 7% from $626 million last year. Surprisingly, sales of paperback books also increased by 6.3%, while hardback books dropped a fraction of a percent. (Audiobook sales continued their steady incline, growing by 25.3%.)
eBook growth has picked up since the last AAP report, which covered the first 3 months of the year, while hardback sales have dropped. This likely reflects general market fluctuations rather than (as I would hope) a sign of serious growth.
Here's all the sales data I received; note that there is a typo in the first chart.