The latest Nautilus designs include plans to rework the places sidebar so that it is more focused and less cluttered. A key part of this design is a new "Add Drive" dialog. This will allow you to permanently add local or remove volumes to the sidebar (removable volumes will be automatically added to and removed from the sidebar, as they are now).

https://raw.github.com/gnome-design-team/gnome-mockups/master/nautilus/nautilus-next/add-drive-dialog.png

The new dialog is intended to replace the existing "Browse Network" item and "Connect to Server" dialog. It has a list of drives, which contains previously used servers, available local drives, and any servers that can be detected on the network.