I don't smoke, but my GF used to smoke (about a pack a day). Then this year for her birthday, she bought herself an e-cig and vaping solutions in an attempt to quit. At first, the flavor she chose was similar to Marlborough cigs, and the nicotine levels were fairly high; she wanted to move off of cigs without much change in anything else. As "backup" she also got a solution of mocha coffee flavor with slightly less nicotine, however she only used the Marlborough solution for a few days before that became the backup and the mocha became her go-to. A few weeks after that, we went to the shop together and she had me pick different nicotine levels for the 2 new solutions she was buying (this time, much more different choosing fruit flavors that had nothing to do with her smoking habit); she wanted me to secretly chose the nicotine levels so that she wouldn't know how much she was smoking. The solution that had the most nicotine that time around was less than half of her mocha. A month after that, she bought some solutions that were just flavoring (no nicotine) and shortly thereafter, she quit completely and has been smoke-free (of either type) for close to 6 months now.
Aside from the money savings and health impact (she says her senses of taste and smell have drastically improved), the one thing she noticed was her addiction behaviors. She no longer has to search her house for a pack of cigs and a lighter before she heads out, nor does she stress if she's out working without the smoking accoutrements.