The 12v high power cable they send out with the cards is problematic to say the least. By problematic I mean they can burn your system, and maybe your house, to the ground.

Followup:

 

Igor's Autopsy of the plug:

Igor's Lab Dissection of the 12VHPWR

 

In a nutshell, it seems the companies Nvidia has sourced their adapters from dont all have the same build quality and the internal design of the plugs is causing breakage internally on the plug channeling all of the power through less wires spiking the resistance across the plugs raising the temps. As Jay points out cables from power supply companies such as Corsair have 1 positive and one negative wire going to each pin socket on the plug making in nearly impossible for this to happen whereas the adapters from Nvidia have the wires soldered to a thin metallic strip that the pins are part of and the strip breaks if too much stress is put on the plug.

Long story short, if you get a 40 series card use a power supply from a company such as Corsair as their cables are safe or from a custom cable manufacturer such as CableMod, who by the way will be offering a metal 90 deg adapter Oct 31st which solves both known issues (cable routing and the melting plugs, to avoid having your PC melt down.