Liquid handsoap (like Softsoap) is generally ok. Most people who do wash the parts tend to use dish soap because it's better at cutting grease. As pointed out above, a soft brush (I use an old toothbrush) is better at getting into the creases. Washing and brushing not only removes mold release agents (if used), but also skin oils and sanding residue. And besides, who wants to paint a dirty figure?
Unless it's a hot and naughty nurse...