I think it could be very handy if you could send files or directories to multiple predefined sites. So for example right click on a folder and transfer to predefined sites. To make this absolutely great you would also need an option to predefine the bookmarks where you would want these files sent to.
To give an example to make this a bit clearer:
you would need an extra dialogue in the preferences or something where you can add the sites to your option "Multiple sites", with existing bookmarks. When you've configured this you have an extra entry in the right click menu called "Multiple sites" And suppose you have a folder called "My files", then you can easily transfer to all the servers you would need to in the correct folders with a simple click. Sounds good heh