Although it's obviously a matter of opinion whether mains cables are worth it to some point, as it can be hard to tell the difference when the cable is installed and the placebo effect may have something to do with lots of people thinking mains cables make a huge difference, I have heard more than one example of people experiencing a weird hum through their amps and not being able to source the problem, only to discover that the problem goes if they unplug their fridge from the mains (Including my own situation, but it was a dehumidifier) or something similar. Surely, then, the audio signal can be affected by noise in the mains path contrary to what some (Keith) people are saying? Obviously a mains cable wouldn't fix this problem and stop noise (maybe a filter would), but if the signal can be affected by noise in the mains then a different cable will have an effect? Even if it wouldn't be greatly beneficial. (Though it may well be.)