This was reported on Ubuntu Launchpad as:
https://launchpad.net/bugs/486315

Distribution:  Xubuntu 9.10

Hello,

The Sub-Pixel smoothed fonts looks different in OpenOffice.org compared to other applications. The fonts look very nice and smooth in GTK+ apps but not in OpenOffice.org Fonts do look anti-aliased, but it appears more blocky for some reason. In order to fix the problem, running the command :

echo "Xft.lcdfilter: lcddefault" >> ~/.Xresources

I think that the fix should be implemented in future versions for a better user experience. Also, if you install Ubuntu instead of Xubuntu, run the OpenOffice.org application, you will not get any font smoothing problems in Xfce installed via xfce4-desktop package. The problem happens when the xubuntu-gdm-theme is installed, which seems to run set-gconf-defaults and causes the problems in font smoothing. Removing the package doesn't fix the problem.

Also, the following doesn't fix the problem :
Removing home folder configuration for xfce, gconf and openoffice.

Finally, I think the reason why this problem isn't in gnome is because it is taken care of via gnome-settings-daemon, something not available in xfce. Ideally, OpenOffice.org should be configured to respect the lcdfilter option, and I don't know how to that properly. But the fix I mentioned seems to be a good workaround, maybe add a script to do that in the package xubuntu-default-settings ?

Additional comments from the reporter:
It happens in other distros with Xfce as well. It might an openoffice issue. I just think you should create a new package called openoffice-xfce or something, which just runs the command. It's a quick and easy fix !