In the old version of papers, I could select several references at once. Then, I could export the bibtex reference (or now citekey) for several papers and past that into a Latex document. Or I could add a tag to multiple papers I had just imported. Some of these options are available if you select one paper, but not if you select multiple.
I have to continue using the old Papers version until you have this because these abilities are central to my to literature review and writing process.
That's exactly the features I'm missing since I'm trying ReadCube… Be able to select several articles and change/add Tags, Author, Journal to all at once (edit Meta Data!). I am able to do it in Papers but couldn' figure it out on readcube. Now I know why… Don't know if I should upgrade… This is very useful on my way to work