Since Ubuntu One has proved to be so brittle, I'm going to try doing the same thing by hand with unison
$ sudo apt-get install unison
on both client and server
Now, say I'm john on both client and server, and I'd like to synchronize the unison directories on the desktops in both the machine I'm working on, and on 192.168.1.2.
$ unison /home/john/Desktop/unison ssh://firstname.lastname@example.org//home/john/Desktop/unison
I've already set up these two machines for passwordless ssh, so that just does it.