If ubuntuone fails to start, is probably due to ubuntuone-preferences. If this ran in a console ends up with:

File "/usr/lib/python2.6/ConfigParser.py", line 311, in get
raise NoSectionError(section)
ConfigParser.NoSectionError: No section: '__main__' 

then it's related to this bug.

Binary package hint: xubuntu-default-settings

Using Xubuntu 10.04 LTS, using the latest available xubuntu-default-settings (10.04.7).

session.sh should not set XDG_CONFIG_DIRS nor XDG_DATA_DIRS.

XDG_CONFIG_DIRS is set by /etc/X11/Xsession.d/60xdg_path-on-session and it fails to include /etc/xdg if XDG_CONFIG_DIRS is already set which in turn is doomed to break a lot of applications (ubuntuone-preferences for example).

Also, XDG_DATA_DIRS is set by startxfce4 and shouldn't be messed with at this early stage.

FIX: comment the lines regarding XDG in /usr/share/xubuntu/session.sh

#export XDG_CONFIG_DIRS=/etc/xdg/xdg-xubuntu
#export XDG_DATA_DIRS=/etc/xdg/xdg-xubuntu
exec startxfce4