gnome-activity-journal not working on Ubuntu 11.04

When launched from the application view, the activity journal doesn't display at all. When run from the shell, I get the following Python backtrace:

$ gnome-activity-journal
Traceback (most recent call last):
  File "/usr/bin/gnome-activity-journal", line 94, in <module>
    from src.main import PortalWindow
  File "/usr/share/gnome-activity-journal/src/main.py", line 30, in <module>
    from activity_widgets import MultiViewContainer, TimelineViewContainer, ThumbViewContainer
  File "/usr/share/gnome-activity-journal/src/activity_widgets.py", line 35, in <module>
    from store import ContentStruct, CLIENT
  File "/usr/share/gnome-activity-journal/src/store.py", line 504, in <module>
    STORE = Store()
  File "/usr/share/gnome-activity-journal/src/store.py", line 367, in __init__
    days_population = ZeitgeistDBusInterface().get_extension("Log", "journal/activity").GetHistogramData()
  File "/usr/lib/pymodules/python2.7/zeitgeist/client.py", line 108, in __getattr__
    raise TypeError("Unknown method name: %s" % name)
TypeError: Unknown method name: GetHistogramData

It looks to me like a required dependency (or a required version of a dependency) is not included as such in the package.

Here's the output of dpkg-query -s gnome-activity-journal, FYI:
$ dpkg-query -s gnome-activity-journal
Package: gnome-activity-journal
Status: install ok installed
Priority: optional
Section: gnome
Installed-Size: 1192
Maintainer: Siegfried-Angel Gevatter Pujals <email address hidden>
Architecture: all
Version: 0.5.0.1-0ubuntu1
Depends: gconf2 (>= 2.28.1-2), python (>= 2.5), python-support (>= 0.90.0), zeitgeist-core (>= 0.4.0+bzr20100718~), python-gtk2, python-gnome2, python-gconf, python-cairo, python-xdg, python-dbus
Recommends: python-gst0.10, python-pygments, zeitgeist (>= 0.4.0+bzr20100718~)
Suggests: tracker (>= 0.8)
Description: graphical user interface for Zeitgeist
 Zeitgeist is a service which logs the user's activities and events (files
 opened, websites visited, conversations hold with other people, etc.) and
 makes the relevant information available to other applications.
 .
 It serves as a comprehensive activity log and also makes it possible to
 determine relationships between items based on usage patterns.
 .
 This package contains the GNOME Activity Journal, a graphical user interface
 which shows a journal of your activities.
Homepage: https://launchpad.net/gnome-activity-journal