I would like to know both the technical and business impediments to
multicasting over the internet.  In particular, why has multicast
penetration stalled as of late: is it due to technical limitations or
is it problems coordinating with all the ISPs and backbone providers. 
Unicast video/audio streaming is gaining increasing popularity but
takes large server/bandwidth resources to maintain and multicast seems
an ideal solution: why is it not being used much?

On a side-note, I know Broadcast.com was following a strategy of
cooperating with ISPs for multicast access; I can't find detailed
information on their business model or technical strategy and would
like that information.  Any information on other attempts by
organizations to provide multicast over the internet or shared
internetwork setting would be helpfull as well.