Major damage? The only damage you could see would be any transfer of files between an external drive used between laptops and desktops that saw any virus infected files. The transfer would then spread the virus effecting Windows.
You could wear out a usb or eSata port from regular plugging and unplugging over a period of time. External drives are made for this type of use to begin with in order to allow moving data and files between laptops to desktops, laptops to laptops, desktops to desktops, etc. there.