It would be very useful, and am thinking of switching to XFCE for the speed.
This instructionswork in 11.10 and earlier
No and yes. There is not one currently supported just for xfce that works (an old one exists, but is broke-see below). However, you can use the "xfce-xfapplet-plugin" xfce plugin (listed in synaptic) to put the "gnome-applet-globalmenu" or the "indicator-applet-appmenu" onto the xfce panel.
See my answer at the following link to add the "gnome-applet-globalmenu" to your setup. The instructions are for the gnome panel, but if you use the the plugin I mentioned above, you can add the "gnome-applet-globalmenu" to your xfce panel. It is a bit flaky. I found the "indicator-applet-appmenu" works better with xfce while the "gnome-applet-globalmenu" works better with the gnome-panel. Your mileage may vary.
The ppa mentioned in the link also adds a listing in synaptic for an "xfce4-global-menu applet", but it does NOT work and according to the README is no longer supported.
Here is a screenshot of it in action (yes, I like a mac-ish look):
Another person has some private code for getting the indicator-appmenu working on Oneiric Ocelot Xubuntu 11.10. I am not sure I yet trust the code for either the ~koshi code or from aaronlewis1989.
In any case, here is a link I found: OMG ! XFCE Global Menu [Oneiric Only]