Is there a minimum length for power cords?

Well, nothing's worse that finding yourself stuck with a pricey cable you cannot use because it is too short to reach the wall socket. I have 3 0f them because I USED to only need 5 feet.

07-07-14: Almarg
Dover, with respect to your comment I don't think a 2 meter or any other precise point of demarcation between what will be seen by the power supply as a stub vs. as part of the loop can be defined. It depends on the specific frequency component of the AC waveform that is being considered. And the distinction will only be relevant, if at all, at the very high frequencies of RF components that may be present in the waveform. With the resulting sonic effects, if any, almost certain to be unpredictable and inconsistent from system to system. I say that regardless of what you may have seen stated in certain marketing literature.

Almarg, my reference was from an engineer, I don't quote marketing hype. I agree the 2metres is arbitrary and I did not claim whether you should hear a difference. I simply stated that the electrical behaviour within the model for a spur is different to a loop.
From my own experience paying attention to power cabling and earth paths can yield significant improvements, particularly in lowering the noise floor and eliminating noise from other components on the "loop" such as video players, TV's etc. As a rule I have found significant improvements from running 1 dedicated line for the whole system, same length power cables for each component to keep the earthing arrangement as close to a star earth as possible to minimise potential differences. I have also found improvements sequencing the order of components as they go into the mains - from source to power amplifier - so the power amps are first off the rank, then pre then source etc. This methodology was proposed by Naim Audio, and I have experimented with it in many installs and found consistent benefits in non Naim systems.

@Yping: FYI, 2.5 meters is eight feet.

I have a 3ft Tara labs cobalt power cord, To my amusment, I sent Tara a E-mail asking about length of this model, Their answer?, The 3ft cobalt will have more resolution period than a 6ft cobalt power cord., that was their answer, However, I can tell you with 515 hours of burn-in that I have now, This power cord is not at all forward sounding, it's presatation is ideal, nor is it recessed, evadently, power cords seem to be different than say, a real short speaker cable where the sound does become forward, as far as speaker cables, I like 6ft speaker cable sound., cheers.