Rubbing alcohol is Ethyl Alcohol with a little water added and a 'wintergreen' smelly additive. The additive (Methyl or Ethyl Salicylate) may attack the plastic but the ethanol won't.
Isopropyl Alcohol shouldn't be rubbed on the skin, but it's a useful cleaning agent if reasonable free of water.
You can buy aerosol case/keyboard cleaners containing Isopropanol and something called Ethyl Cellosolve to remove the usual oily crap that builds up. This won't whiten a yellowed case though.
Nail varnish remover contains acetone which will almost definitely attack/dissolve the plastic used for keyboards.
[EDIT]Rain water is essentially distilled ('pure') water, which will eventually remove filth by abrasion and mechanical flushing. When it dries, there's no salty residue to cause short circuits. Tap water conducts electricity due to dissolved salts, which are left behind as a white deposit. That can cause shorting.[/EDIT]
People claim that bleaching the keyboard parts with Domestos in the dishwasher works, but I think it could embrittle the plastic. The plastic goes yellow through atmospheric oxidation. It happens in the dark, but is accelerated by sunlight. The outer few microns of plastic could be abraided off by hand using wire wool, but the most certain way to get a yellow case/keyboard back to buff is to use a plastic paint aerosol.
JaX
