windows systray-icon behaviour
I would like to suggest a change in the (click-)behavior of the trayicon. Most Windows applications with a trayicon show/hide their main window when (double-)clicked.
Calibre however restores the application as it was before, that is if it was minimized to the taskbar it will just show/hide the taskbar icon. In my opinion that is not the expected behavior of a trayicon.
Also perhaps an option of "minimize to tray" (instead of to taskbar) would be nice.