This is how Nautilus Elementary looks without the tweak:
This will make the main toolbar the same color as the titlebar/menubar, add breadcrumbs, redesigned sidebar and more.
To install it, download the archive from DeviantArt, extract it, then press ALT + F2 and enter: "gksu nautilus", then navigate to /usr/share/themes/Ambiance/gtk-2.0/apps/ and paste the "nautilus.rc" file and the "nautilus" folder from the extracted archive (press 'Yes' when asked if you want to overwrite the original files).
Then switch to a different theme and then switch back to Ambiance.
To revert the changes, open a terminal and copy/paste the following command:
sudo apt-get install --reinstall light-themes
Then once again switch to a different theme and then back to Ambiance.
Thanks to Victor for the tip!