As a Kindle fan, I'd say e-book sales slipping are easily attributable to the fact that there is so much free content out there for e-readers that people are reading the free stuff and not buying. I think a significant test would be comparing library check-outs to ebooks to print sales. (Figuring out a test that isn't skewed would be hard, but let's handwave that away). I wonder if you'd see that 'e-book reading' people who used to check out lots of books from the library have dropped off and are just reading free books from e-book stores?