It would be great if a plugin could integrate the Send to Kindle app into Calibre so you could just press that button and the Send to Kindle interface came up. This would be a great way to send multiple books without having to attach the Kindle to the PC or open many folders to get the mobi files. The nice thing about Send to Kindle is it will store the file in your Amazon archive so the books are available to all your Amazon devices and you can send to as many Amazon devices as you have registered all at once if you like. I don't know if this is possible but hope so.