It can't be good what you're inhaling, no. There must be some ionising going on with the vapour because it's electronic I guess and if your liquid tank is dry you smoke really toxic burned, maybe synthetic stuff. The things don't even prevent you from inhaling that (mustn't be too hard to add a fuse-like thing, surely).

Apparently (I just heard about this on the news or something) electronic cars also produce very toxic vapour. It could be far worse than petrol fumes.

But as long as your immune system keeps working (probably overtime), it at least blocks up oxygen passage in your lungs less.