I wonder how many people are unable to use multicast because
it's not available to them for one reason or another.
I find that I'm unable to use multicast due to our site's unhappy
choice to install some cisco equipment that doesn't support it
without using cisco proprietary protocols - which our admins
don't understand and are therefore reluctant to enable.
I had much the same experience. Years ago we had routers that supported
multicast and I was actually able to participate in an IETF (Munich?)
using it. Then we got new equipment and one of the things we lost in the
upgrade was multicast support.
Ned