Metadata based discovery and browsing have been a strength of libraries; without the motivation to sell copies, many cost-free e-books lack even basic metadata, let alone good quality catalog records. This is clearly an area where libraries can make significant contributions, especially when they work cooperatively.
With a flood of free content already available, and much more on the way, there is a continuing need to highlight the material most suited to the needs of the user. Multiple editions can exist of public domain works; it makes sense for libraries to help patrons find the best ones.
Perhaps the best example to date of work in a library on selection and description of open-access e-books is the Online Books Page at the University of Pennsylvania. Edited by John Mark Ockerbloom, it indexes over a million online books, all of them available for free to users.