Actually it's around 6% loss in lines and transformers: 2% in transmission and 4% in distribution.[1] This works out to be quite a lot. In some high-intensity areas, Ohm's law losses can use more energy than refrigerating a superconductor over the same length. I'm not sure that there exist ways of increasing efficiency here, but getting another percent or two of global energy production for "free" would be amazing.

But I'm not really sure that the distribution network is holding Tesla back right now. With some SolarCity and a PowerWall, you're going to be able to go off-grid. In theory. The idea is to be a total alternative to traditional energy companies and utilities.

[1]: http://insideenergy.org/2015/11/06/lost-in-transmission-how-...