Personally, I think it might be a good idea to ban them until they can really come up with a relatively safe "Nicotine only" e-cig. Here is an excerpt from the surgeon general's report:
"Besides nicotine, e-cigarettes can contain harmful and potentially harmful ingredients, including:
ultrafine particles that can be inhaled deep into the lungs
flavorants such as diacetyl, a chemical linked to serious lung disease
volatile organic compounds
heavy metals, such as nickel, tin, and lead"