Meme, you've likely had a lot of feature requests you had to ignore. Here is one more.
As you've created a GUI for some facets of managing the Kindle, would it be possible to add a checkbox for "Keep this item"? I often load some of my backlog of calibre site downloads onto the kindle, but unless I laboriously set each item to "Keep this item" on the kindle, they're gone the next day.
With a gui, or some other way to set the flag from calibre, my playing bulk catchup on sites would be made much easier.
Thanks for considering this. Actual implementation of course depends on how tough it is.