Reading a book at home or on the beach is a pretty anonymous activity but as soon as eBooks are used your anonymity is traded for convenience. When you download a book it is linked to your account. Because books are tied to a user's account, removing them from one's device often means the original record will still exist and every e-reader is capable of tracking your reading page by page, your bookmarks and highlights– most of this is for our benefit and we like it but we should be aware.
At the end of 2012 the Electronic Frontier Foundation - a US donor-funded nonprofit that aims to defend the individuals’ digital rights - published an E-Reader Privacy Chart. Almost every eBook service tracks searches for books, meaning not just what you read, but what you're interested in, is stored. On this chart Overdrive rates quite well. To look at the Privacy Chart click here.