Got a notice on this via NetGalley -- if you upgrade your Kindle App on iOS (iPad or iPhone, etc), the current version has a bug that will delete all of your existing books on the device AND all your bookmarks and notes. The good news is, if this happens to you, you can redownload your books and your notes and bookmarks that have been backed up should be downloaded with them. For those who don't have the app already installed, you can download the current version without issue, but Amazon has issued a warning not to upgrade for existing users. A new version is on the way (and hopefully will fix the problem). More info can be read over on CNET.