I love it!
One thing I would like, is that the xml files produced would beeasy to syncronise. I would suggest that for a map file there be an option to include a UUID (or any kind of <i>unique</i> id) and last modified date (preferably a simple seconds since epoch string) with <i>every</i> node. An external sync program would be able to take a file from two hosts and update nodes according to the last modified dates.
It would be cool to have a "mind-server" - A simple server that actually held the map info. freemind would then either not hold any data but talk to the server for it's data, or would cache that info. This connection could be local, or remote... and there can be many connections. We could even make the servers do the syncing. This way multiple people can work on it, connected or not.
It would probably help that you could set node-tags like "owner" and "distribution-limit" "write-limit" etc.