According to http://www.arnnet.com.au/article/362617/aiia_nbn_crucial_making_australia_greener/ the nbn will make a significant environmental impact!
Apparently there are some aging data centres around which take up prime realestate as well as drawing power from the energy grid. These centres would likely be consolidated into newer more energy efficient centres.
Not to mention you could have much better teleconferencing, saving on travel... reduce paper wastage by sending large documents electronically...
I wonder if in 10 years time we'll look back and think who were the idiots opposing the NBN?