Virtual & Real(ity)

Gaming is already well known. Gaming engines are currently applied as user interfaces to show the real world. Of course, we still have virtual worlds like second life, but real worlds are slowly taken up. Take for instance various cities that present themselves on the web by showing 3D buildings. The next step will be to integrate traffic simulation models in these environments. Chatting and voice is already becoming available, so what will be the difference between virtual and real?