I found that having one single PC or Laptop with one calibre library works fine. You can search and complete your ebook metadata so you have a clean ebook library with authors, comments, ISBN, rating and so on filled in....
It gets messy, when you need one basic software functionality: to export and import a ebook together with their covers and already filled in metadata from another calibre database.
This is not implemented yet and it seems, that synchronizing two libraries are not foreseen as well. The two ebook libraries run out of synchronization, so you have to do everything manually on the second Computer, what you already inputted on your first PC to add there the same new book too.
So basically your two calibre libraries on two computers run out synch. If you want to add one ebook you have to do it twice because the Metadata *.opt file and the cover picture is ignored when importing into the second library.
Is there anything in the future planned to deal with that Metadata and cover importing feature into another calibre library ?
It cannot be that you have no possibility to get things out of one calibre database and import it into the next calibre database - is it so hard to implement ?!
Please make it happen in the future, then I will love and use calibre again.