Originally Posted by Brink
This old electronics tinkerer has a problem with this. Mr Ohm's Law says that for 100W at 5 volts, you need 20A of current. 20A of current through those dinky USB cables would melt them, (and potentially set your PC or desk on fire) as the wires are small. The cross section of the contacts in the USB plug aren't big enough for that kind of current either, inserting and de-inserting them would risk welding them.
Unless they intend to bump up the voltage, I can't see how this is going to work with new cables, let alone existing ones.