There certainly has, but because it's a comparitively new product it's hard to gauge if there are any long-term effects. So far, it's generally regarded as "magnitudes safer than smoking", which is good enough for me.
As a night-out tool, I think it makes good sense (someone I work with does the same to stay off the fags, but doesn't vape otherwise). For that I would suggest a simple Ego battery and mini protank atomiser combination. Will easily last the night if you get a 950mah battery, while still being small and light enough to fit comfortably in your pocket while you cut some rug on the dance floor.