I've been using an electronic cigarette for approximately one year now. I haven't had any negatives to say about it except that they should have become mainstream a long time ago. They cost money, but they fall in costing way less than regular cigarettes. My sense of smell and taste is now back where it used to be, my fingers and clothes no longer stink, no dirty ashtrays to deal with, ect. Every blue moon i'll get the urge to smoke a real one, so i'll light one up and and not even take more than a drag off of it before snuffing it out. They taste horrible now!
From what I've observed with the laws popping up concerning them, it has to do with the odd individuals that smoke them with the intention of creating huge clouds of vapor... becoming a nuisance. More often than not, it's the people that use zero nicotine which are the ones creating the nuisance in public places.
The only health risks are tied to where you source your liquid from. If you purchase it from a reputable company which explicitly lists the ingredients, you know what's in it. If someone is purchasing it from 'Joe Blow's Homemade Liquid' who makes it in their back yard, there's no telling what's in it. In a nut shell; regulation of ingredients.
Like anything else in this world, know what it is before you eat it (or smoke it).