How to add/remove buttons to Nautilus toolbar?
10.04/10.10/11.04
It can be done in a hacky way by editing /usr/share/nautilus/ui/nautilus-navigation-window-ui.xml. You'll want to look into the part that begins with <toolbar name="Toolbar">.
There is no option to customize the toolbar, but there is a bug report requesting it. Feel free to increase the bug's visibility using the "This bug affects me" feature.