That's a good question. It's a question that politicians are running with and trying to pass legislation on.

Basically, cigarettes are a nicotine delivery system. Nicotine in large quantities is lethal, no bones about it. However, large quantities for nicotine is minute compared to other stuff. Anyway, most of the carcinogens in cigarettes are formed during the burning process, and there are a shitload of carcinogens in cigarette smoke.

More testing needs to be done on e-cigarettes to determine their potential danger, as they are relatively new. But, one obvious advantage is that there is no burning plant matter from which carcinogens can form. Additionally, the ingredients that make up e-liquid (the stuff that vaporizes) is relatively well understood. Yes, the nicotine can cause cancer, as can one of the common sweeteners for e-liquid. In general, it is thought that e-cigs are a vast improvement over traditional or "analog" cigarettes. Also, the vapor dissipates much more readily into air, because there is less stuff that comprises it.

So, in short: e-cigs are less bullshit than people assume. There are people who think that they are completely safe, but the fact is that consuming nicotine is not completely safe. However, there have been studies done that equate the risk of nicotine from e-cigs to the risk of consuming caffeine from coffee, something which few people consider to be a danger even though it's relatively easy to overdose on caffeine.

The ones you see on TV, I imagine are what the vaping community terms, "cigalikes" or, vaporizers that look like cigarettes. I don't know much about those. Actually, I got on e-cigs because of a post I made on hubski a while back. AlderaanDuran and insomniasexx seem to know more about (or at least have more experience than I do) with e-cigs. Maybe they can chime in to more fully answer your question.