Personally, I don't
envisage e-cigs "catching on"
BIG style in the long-term.

... they're
weirsh, tasteless things - which most definitely
cannot replace the satisfaction to be derived from
proper tobacco products.
Admittedly ...

...
I've partially sampled only one - bought in the local Poundland store - but it offered me so little satisfaction that it's lain
(otherwise) untouched in a kitchen cupboard for months now
!