Re ubuntuone and xubuntu - sounds very similar to this question and answer: Ubuntu One for Xfce or Xubuntu?
Its been tidied up in 11.04 so that you dont have to install all the Gnome dependencies and other Gnome files
To summarise - use Software Centre and search for "UbuntuOne".
If you want to use the terminal so that you are content to see all the additional packages being installed then
sudo apt-get install ubuntuone-control-panel-gtk
This will install the main control panel & other services to allow you to sync with the UbuntuOne folder in your Home folder.
To launch the Control Centre - create a menu link to run /usr/bin/ubuntuone-control-panel-gtk