It's best suited for applications which may join or leave at any time. PGM uses UDP transport but implements TCP like features for reliability. The big word on Wall Street is to invest in anything that is remotely associated with fiber-optic networks. To some degree this is true. But the next big revolution in networking since the introduction of the World Wide Web is IP multicasting.
Every corporate enterprise wants it in their network.
However, supporting ISPs trying to accommodate the explosive demand are becoming increasingly frustrated. It's here already and probably on your network. This technology has been around since 1980, the creation of a post graduate student, Dr. Steve Deering. Today, multicast is everywhere. You probably listen to radio stations at work on your laptop via a multicast connection.