The problem is very simple. 99.99% of Users in the united states DO NOT HAVE THE UPSTREAM BANDWIDTH to do anything cool with .mac.
I can tell you something however... Apple has thought about this... How do we get a user to back up their entire drive on the net? Stream large movies? Peer2Peer. Apple plans to build a network where people can share upload bandwidth so that uploading and moving large packets of information around become easier.
Until then even uploading a 50mb file for back with .mac sync times out, often because a broadband provider like comcast, times out, or people will start using downstream at the same time and have problems with it.
.Mac Needs to Be Radically Retooled