Hello,
Your story about the back EMF of a coil is true; you can get high, even lethal, voltage out of it. But voltage is not same as energy.
Energy is voltage*current*time product. The voltage spike you get is of short duration and current is less or same as DC current before interrupting the current. The "voltage spike out of an inductor" is used in the "boost converter". This SMPS (switched mode power supply) circuit converts DC low voltage into DC high(er) voltage (but with less output current). These circuits can operate with efficiency > 90%.
The inductor in the boost converter circuit is used as temporary energy storage, however over time the inductor doesn't generate energy.
The same is valid for a permanent magnet. There is energy in the field (supplied during the production of the magnet). The amount is low (think of mJ), when you use it, the field is gone (so you don't have a magnet anymore).
As mentioned before, you can use a magnetic field to convert mechanical energy into electrical energy, and the other way around, but you don't get more then you put in.
When 1000 people say something, it doesn't mean it is true. As far as I know there is no perpetuum mobile.