As a teacher at an architecture school, this virtual worlds/virtual building connection also interests me.
We have been doing some research work at the university on a Second Life environment, that I find very promising.
It allows for collaborative design, and, as an immersible interface, it is much more powerful than the archicad 3d window.
My firm belief is that the interface is moving in this direction.
Some years ago I talked to Graphisoft about this (using caves, 3D wands, etc.) and their simple answer was "is there a market for this".
I have come to understand that there is not. Yet.
This, I believe, could be a great business opportunity.
Anyway, if you want to read a bit about my vision, please read this short story:
http://bimania.blogspot.com/2006/10/archicad-18.html
Best of luck