Smoking of a regular cigarette on Yom tov is forbidden for 2 reasons.
1 It harms a person's health and is forbidden all year round
2 It is forbidden on Yom Tov because of the principle that it is not שוה לכל נפש.
See Mishna Brura and Beur Halacha to Siman 511, Halacha 4.
Although in the days of the Mishna Brura where it was very common for all types of people to smoke, then in his days there was a difference among the poskim if Smoking is allowed on Yom Tov.
Now that many people do not smoke, all or almost all poskim would forbid smoking on Yom Tov based on the principle brought by Beur Halacha.
Even after reading about an electronic cigarette on wikipedia I still don't have a firm idea what it is, having , thank G-d never seen it being used.
But I doubt its law would be any different than the normal cigarette.