I know that that it's not Ubuntu's fault that the gnome-devs have removed so much of the useful functionality from nautilus 3.6, but one regression that I find particularly annoying is that the backspace key no longer works as a 'back' button. Instead, you have to press ALT-left arrow, which is much more complex, as well as non-intuitive (non-intuitive in the sense that many users tend to use backspace to go back in browsers).
DistroRelease: Ubuntu 13.04
Package: nautilus 1:3.6.3-0ubuntu5
ProcVersionSignature: Ubuntu 3.8.0-2.6-generic 3.8.0-rc4
Uname: Linux 3.8.0-2-generic x86_64
Date: Tue Jan 29 15:39:50 2013
GsettingsChanges: b'org.gnome.nautilus.window-state' b'geometry' b"'800x550+853+1291'"
InstallationDate: Installed on 2012-08-25 (156 days ago)
InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Alpha amd64 (20120724.2)
UpgradeStatus: No upgrade log present (probably fresh install)