I'm not allowed because I work in a dry cleaners and any kind of smell in there can put off the customers, even a very faint, nice smell. That said, I cover the shop by myself on my manager's day off, so he would never know!
My uni bans ecigs anywhere other than the smoking shelter. I've only made the switch during the Easter break, but I'll mostly stick to this rule as I don't want to get told off. Only mostly because I did used to smoke in other (outside) places sometimes, and will probably vape even more in those situations, as it's a lot less likely to get noticed due to the lack of smoke smell.