My husband has been using them for just over a year and he uses this beast
http://www.go-liquid.co.uk/Store/e-cig-devices/vamo-v5-kit.html, has done now for well over half a year (the same one). He has 2 rechargeable batteries and each one lasts him a couple of days but they are starting to age so he might replace them soon.
Are they healthier? Well nothing has been set in stone but it is the crap in the cigs that cause the damage,
not the nicotine (it's actually on par with caffeine), ecigs don't contain crap, they don't smell like crap and don't make everthing/everyone else smell like crap so I am happy that he uses this rather than regular cigs. He tried to stop so many times but fallen off the wagon each time.
A lot of the flavours taste nice too but he tends to go for menthol as the fruit/chocolate flavours can become sickly.