||07-27-2011 07:54 AM
Let me make sure I'm clear on my terms and separate the purpose of the wire from the marking of the wire/insulation.
I know of no reason why you would switch neutral. Neutral should always be on a white wire (unless > 6 AWG) but a white wire may not always be neutral. You are permitted to reidentify a white wire as a hot (normally with either a wrap of black electrical tape at both ends or a sharpie) if it's part of a cable or > 6 AWG and you have a reason to do so. An example of when you might do this is if the switch was after the outlet in the circuit (see here for a diagram). In this case, although the insulation is white (remarked as a black) the wire is actually functioning as a hot since it's between hot in the panel and hot at the outlet.
I redrew the diagram from the above-linked site to make it a little simpler. Current moves clockwise: