It varies. Newer e-cigarette devices can deliver substantial amounts of nicotine, and some users are able to get nicotine at levels similar to or even greater than a traditional cigarette.
Some research has found that e-cigarettes deliver less nicotine on average than traditional cigarettes, but that users may change puffing patterns to compensate. Inexperienced e-cigarette users take in modest nicotine concentrations, but those who regularly use these devices adjust their puffing to consume similar levels of the drug as with traditional cigarettes.