@stefan,
This comment is in hopes of being invited to beta. I have been using Mendeley (desktop and mobile) and am now switching to Paperpile. I would really like to be able to use the Android mobile version so that I can read papers on my Android tablet.
I know this is in Beta but having the opportunity to at least read my .pdfs from the app would be great. I would also like to provide feedback on the newer features as they are added.
So please invite me I would like to do quite a bit of reading on my tablet (and annotations when they are available).