If money savings is a potential draw for you, sure, e-cig cartridges are far cheaper than cigarettes. If you fill your own cartridges, however, it’s even cheaper. You can buy the “e-liquid” premixed, with nicotine, flavoring, and base, or you can buy the above ingredients and mix your own.
Filling your own cartridges will you give a much more satisfying puff, will generally allow you to go longer on a cartridge, and of course is more environmentally friendly. I don’t have a cite for just how much cheaper, but to put it into perspective: I just placed an order the other day for supplies to make about half a liter of e-liquid. This should last me 250-300 days. It cost me about $30.
Even with replacing atomizers, batteries, etc, it’ll cost me under $100 a year to smoke. It would cost me around $3.2k a year here in Rhode Island for a pack a day habit.
As far as downsides that you asked about, that’s not entirely known, really. Obviously people have been inhaling nicotine for many many years, and the effects of that are well known. The base of the liquid is generally either food-grade vegetable glycerin or propylene glycol. I’m not aware of any definitive studies on the long term effects of inhaling the vapor of either of these.
There’s definitely no tar or any of the other myriad nasty chemicals, though. Another downside is that many folks don’t find it as satisfying as smoking a cigarette, but that is entirely subjective. Careful selection of your setup goes a long way, though. For example, I use a low resistance atomizer. This will cut down your battery life, but they heat up faster and hotter, resulting in a warmer and fuller puff, more like an actual cigarette.
I won’t ramble on about them, so I’ll point you to an e-cig forum where you can find a wealth of info: http://www.e-cigarette-forum.com