It's not just facts 'n' stats by any means, but here are some anyway:
According to the 2011 Library Journal E-Book Survey, 82% of libraries currently offer access to e-books, which reflects an increase of 10 percentage points from 2010. … Libraries maintain an average of 4,350 e-book copies in a collection.
[T]he publisher-to-library market across all formats and all libraries (e.g., private, public, governmental, academic, research, etc.) is approximately $1.9B; of this, the market for public libraries is approximately $850M
92% of libraries use OverDrive as their e-book dealer
Of the major publishers, only Random House allows unrestricted lending of e-books.
I found the section on business models to be particularly clarifying.