Some transformers can have high efficiency when running at light loads - but that means you just paid extra for an oversized transformer. In general, copper losses go up with the square of load current and iron (core) losses go up with the square of voltage. Of course a 30MW transformer will be designed for higher efficiencies - no one wants to pay for 10MW of losses or deal with all that heat.
Compared to gasoline (according to wikipedia), 300kJ is about 0.01 Liters of gasoline = about 1 cent worth. So 1 penny worth of kinetic energy is lost every time you have to emergency stop on the freeway with your SUV? At normal highway speeds its less than half that energy (E=1/2 m v^2).
That's the beauty of MPEG4/DivX/VC1,etc - they are much more efficient than MPEG2 (standard DVD encoding) - you can actually fit HD quality movies on a regular DVD (as mentioned earlier).