Xerox still holds this patent and I think one company (Inxight?)
licensed the technology exclusively for their data visualization
software. Vladimir Bulatov did an open-source Java Profile Browser
HyperProf(1) and got spanked by the patent holder (or licensee). He had
to remove the source code from his web site, but because of the
non-profit nature was allowed to leave an applet as a demo. On the other
hand there are no such things as software patents in Europe (until
now(3)) and the open-source project HyperTree(2) is using this as legal
ground for their work. 

Alex

(1) http://www.physics.orst.edu/~bulatov/HyperProf/
(2) http://hypertree.sourceforge.net/
(3) http://petition.eurolinux.org/index_html?LANG=en
(4) http://www.inxight.com