DOCBOOK-APPS: xml diff tools

Hi,
Just wondering if anyone had any thoughts or suggestions about xml diff
type tools. I'm familiar with standard diff and the cvs tools but
wondering if a tool like xmldiff would help for collaborating in a
non-connected environment like editing and returning the edited copy.
Is anybody doing anything similar and using any of these Free Software
tools?

An example:
http://www.logilab.org/xmldiff/

I know there is also a changebar type feature to the stylesheets but I'm
not sure how to use or edit docbook to get it to work. Does anybody use
this feature?

Thanks for any help,
Eric