Comment 7 for bug 545894

dezza@Demetria:~$ apt-cache policy gnome-screensaver
gnome-screensaver:
  Installed: (none)
  Candidate: 2.30.0-0ubuntu2
  Version table:
     2.30.0-0ubuntu2 0
        500 http://mirror.as29550.net/archive.ubuntu.com/ lucid-updates/main Packages
     2.30.0-0ubuntu1 0
        500 http://mirror.as29550.net/archive.ubuntu.com/ lucid/main Packages
dezza@Demetria:~$ apt-cache policy xscreensaver
xscreensaver:
  Installed: 5.10-3ubuntu4
  Candidate: 5.10-3ubuntu4
  Version table:
 *** 5.10-3ubuntu4 0
        500 http://mirror.as29550.net/archive.ubuntu.com/ lucid/main Packages
        100 /var/lib/dpkg/status
dezza@Demetria:~$

I've noticed that it's not just limited to libnotify. Skype and Thunderbird pop-ups also appear over the screensaver.