I sent this suggestion to the original poster of the thread and it
may have become lost:
Project proposal: integrate Suse DeltaRPM software with yum to improve
bandwidth efficiency when updating a distribution. I've experimented
with this and I've got good results
(see
http://www.wombat.ie/software/rpmdc/manual.html ). However my
implementation is heavy, requiring Java, Tomcat etc.
Joe.