From the PING Review:

A lingering question and concern for me is how interaction will take
place between reading an EPUB ebook and browsing the Web more
generally. If a reader taps on a link in an ebook, will any
information about the ebook (or personal information about the reader
who purchased the ebook) be passed on to the target website of that
link? Or will there be links between ebooks or from a website into a
particular page on an ebook?