how to fix your screensaver after ubuntu oneiric ocelot or later wipes
xscreensaver out:

this page has good info about most of what's needed:
  http://www.webupd8.org/2011/10/things-to-tweak-after-installing-ubuntu.html

this page shows how to get menu working again:
  http://ubuntuforums.org/showthread.php?t=1865593


this directory also has a file containing a slightly modified version of the
fix for the gnome screenlock menu item.  it's called screenlock_dbus.py.