Many years ago I was the MCI side of the Real Broadcast Network. Real Networks arranged to broadcast a Rolling Stones concert. We had the ability to multicast on the Mbone and unicast from Real Networks caches. We figured that we'd get a hit rate of 70% multicast (those who wanted to see the event as it happened) and 30% unicast (those who would wait and watch it later).
You do realize that unicast from Real Networks caches *IS* multicast, just not IP Multicast. Akamai runs a very large and successful multicast network which shows that there is great demand for multicast services, just not the low level kind provided by IP Multicast. In fact, the most important use for IP Multicast is to work around the problem of the "best route". In the financial industry, they don't want their traffic to take the best route, because that creates a chain of single points of failure. So instead, they build two multicast trees, send a copy of each packet into each tree, and arrange that the paths which the trees use are entirely separate. That means separacy of circuits and routers and switches. -- Michael Dillon