Simply running startxfce4 always gives me this:

** (xfdesktop:58928): CRITICAL **: XfceDesktopMenu init failed (The XfceDesktopMenu module could not be loaded: dlopen(/opt/local/lib/xfce4/modules/xfce4_desktop_menu.so, 10): Symbol not found: _desktop_menuspec_path_free
  Referenced from: /opt/local/lib/xfce4/modules/xfce4_desktop_menu.so
  Expected in: flat namespace
)

Unfortunately, the "Xfce logo loading screen" obscures my terminal, so I can't say whether the error is raised during that, or when the "loading screen" suddenly disappears and leaves me with no desktop.  

/opt/local/ comes from the fact I installed Xfce 4.4.2 with MacPorts 1.600.

Specs:
Mac OS X 10.5.2 / Darwin 9.2.1 (Intel)
X11.app 2.1.1 - (xorg-server 1.3.0-apple5)