Safety concerns using metal switches near 300V (low current) lines?
I have on my desk some of these ordinary toggle switches.

The datasheet reports "Insulation resistance: 1000M ohm min" and "Dielectric strength: 1000V RMS min @ sea level". The latter is the figure of merit, telling you that it's guaranteed to contain voltages up to 1kV without breaking through the insulation.

However, if you look around you, you won't see very many products with metal toggle switches on. This is because the normal technique for avoiding this problem is double insulation : http://en.wikipedia.org/wiki/Appliance_classes ; you'll see plastic toggle switches, or plastic buttons, or (in one case I saw) a switch internal to the case operated by a plastic lever from the outside switch. (The IEC standards are probably the "long answer" to all questions about electrical safety engineering).

Capacitative sensing has also become more popular, as it can operate through a thin plastic insulated case and avoid all this hassle.