As someone who got into e-cigs relatively early (2009) and still vapes, it's important to note that they are NOT really meant for quitting. Sure, it's possible to quit using them, but they are more intended to be a replacement device. It's only quitting in the sense that you're not using traditional cigarettes anymore.
Why are they catching on?
1. They are (likely to be) healthier. Sure, some will say that e-cigs contain ingredients present in anti-freeze. These same ingredients, though, are also found in rescue inhalers, fog machines, and Twinkies. Mostly, though, they don't contain all of the tar and poisonous substances we all know are present in other cigarettes.
2. You don't smell like burnt paper, and don't make you smell like burnt paper for the rest of the day. Pretty self-explanatory.
3. (Or 2a) You can vape indoors, and stealth-vape. Smoking outdoors is fine eight months of the year here in Upstate NY. The other four months - and all of the days it's raining - having to go outdoors sucks. Not only in homes and apartments, but at bars. Also, if I'm in a place where I don't want people to know I vape, I can just go into the bathroom or a toilet stall, and nobody is the wiser. Not the same for a cigarette.
4. Much easier to maintain a constant buzz. I recently had the charger I've had since the start decide to stop working, so I switched back to traditional cigarettes. I absolutely hated that I felt like hell or got enough of a buzz to make my legs weak.