The problem with Tessla's vision is summed up in one word; "interference".
Make a tessla-coil (a high power version of those zappy glow globe things that follow your fingers on the glass) and turn it on anywhere near a TV, Radio, wireless networking device, mobile phone etc...
You will get very noticeable signal noise. At the science fair at school I made one and I was only allowed to run it for 3 minutes every 15 minutes, because it interfered with half the other exhibits.
Energy "beaming" like this could be very useful for sending power to remote devices or vice versa allowing for tiny remote surveillance devices that don't need a power pack.
Interestingly enough due to general electrical imbalance in the earth, caused by things like power lines, lightning, other general electrostatic build up, chemical energy and energised particles flying through space there is enough ambient energy that when combined with the power of a radio transmission signal, and forced to all go in the same direction by a diode you can make a basic AM radio reciever (crystal radio). All you need to do is ground it to something well earthed like a metal pole or even ground water (water pipes work well).
