One more thing - cats are very bad in metabolizing scent. It is something of an anomaly with them and highly scented environments can give them liver damage.
That isn't just related to e-cigs, also air fresheners and Plug Ins should be avoided around cats. I learned that when I did my cosmetics course, so Mr Cat is always banned outside while I am pouring Candles or when I make soap (also because most people don't appreciate finding cat hair in their produce). Plug Ins and Joss sticks are the worst for them, Febreeze is ok-ish, as long as you don't spray it where they sleep. (if your cat is anything like mine, that means you can only Frebreeze the bath tub)