For years, high concept action films have been sold to movie studios with one or two line pitches which encapsulate everything worth knowing. For example, for the film Days of Thunder, "Top Gun meets Nascar".
Whenever anyone talks about the next step for the internet, and new technology, it's good practice to use the same rationale. For instance, web 2.0's Wikipedia "An online encyclopedia everyone can contribute to'.
Web 3.0 seems to revolve around an online world in 3D, but noone seems to have come up with any reason why 3D would be preferable to 2D for anything other than gaming.
And the best example of this I've found is 3DMailbox, which you can see in more detail on TheWayoftheWeb, here.
If it isn't easier, quicker, better, or more fun, then why do it?