One of the primary reasons I stayed with paper books after ebooks were introduced was because I heavily annotate my reading material.
Once Kindle allowed highlighting and notes, my resistance to ebooks was overcome by my newfound ability to digitally store annotations over time.
While Kindle allows for digital notes, unfortunately, Kindle does not have an API for the annotations. Fortunately, speric's ruby.gem called 'kindle-highlights' is a workaround to capture Kindle Highlights, and the results are below.