chadh,
It's an accepted fact even outside the audio community that you don't want to mix wiring used for house current with low voltage wiring as the electro-magnetic and radio frequencies interferences from the house current will affect low voltage signals. As power cords must be insulated, they might as well be shielded as well.
A good rule of thumb would be to avoid parallel runs of each (provide 12 inches of separation if you can't avoid) and if they come close to each other try to make them "cross" at 90 degree angles. As each installation varies, some won't have these problems or they won't be as apparent.
