A few short articles about 2012 sales figures:
Ebooks now 1/5 of US book sales: Mashable
Ebooks account for nearly 1 billion in trade growth: Digital Book World
Ebooks account for 20% of US books sales in 2012: Good E-Reader
An interesting point about the above three articles is each respective author (or website editor) has his or her own way to spell “e-book.” I have struggled with this myself, mainly because there appears to be a kind of view emerging that the “camel-case” (or CamelCase) spelling – “eBook” – is “classier.” I think this is happening because people have become too influenced by brand spelling (iPhone, PowerPoint, AstroTurf, et cetera). However, it is incorrect. Forcing a lower-case “e” also looks horrible at the beginning of a sentence. If it is not a proper noun, one must be able to capitalize it at the beginning of a sentence. “EBook?” No.
Most dictionaries agree that the hyphenated “e-book” is the correct spelling. This is OK, but just as “e-mail” is now usually spelled “email,” I think “ebooks” will emerge as the standard. “E-reader” and “e-ink” will likely follow the same path. Note that the term “E Ink” with no hyphen is a
brand company name, and I think the camel-case spelling “eReader” belongs to Kobo.