I hope this doesn't fall on deaf ears. Here are a few improvements that I think would really add to Calibre's usefulness.
1. Latest import view. List of books imported in this session. A nice addition feature would be to have items removed from view if they get edited.
2. Highlight & note manager. First off, the calibre viewer needs to have the ability of saving notes and highlights (if it already does, how?). These notes should be manageable & exportable, and you should be able to import from kindle mbp files (the current 'get annotations' feature is pretty much useless for anybody who makes more than just one or two highlights)
3. Function to search within ebook to auto-discover ISBN.
4. More user friendly cover image scraper? Perhaps give the user a list of multiple cover versions found online and allow them to select the best/right one.
5. A book cover browser that is more functional and less flashy than the current 3d flipbook cover browser. A simulated bookshelf would be 92133735463 times better.
6. Global search with paragraph context results. It would be amazing if Calibre could index all the ebooks so that you could quickly search your entire library and get search-engine styled results with the text surrounding found keywords.