The fact is that gnome can't start if it doesn't find gnome-screensaver. It shows the infamous "Something has gone wrong", and other than that, it offers no hint to the average user about what's going wrong. Unless someone wants to dig into this and patch it to work without gnome-screensaver, I suggest adding it as a runtime dependency.
What GNOME version? (e.g, gnome-session version)
Sorry to have been so short in details, gnome-session is 3.6.2-r2. The kdm log doesn't provide much more info, and so doesn't the .xsession-errors file, but I can attach them if you think it's worth something. Thank you-
This is no longer needed in 3.8 (gnome-screensaver was dropped)