Not really much statisically, but to add to the anecdotal data, here ya go:

Grandad always used Zippos. He smoked every day, so for him it was not any extra effort to remember to recharge the lighter once a week. When he bought cigarettes, he would be sure to buy his lighter fluid or his flints if he needed any. There were a couple times he'd gotten it wet and the flint wouldn't strike a spark for a bit. As for me, I don't smoke anymore, and so sometimes I remember to resupply the zippo, sometimes I forget. Since I don't use it much ( I have a refillable butane lighter that gets the most use), it consequently isn't always usable for me. If I am mission oriented, then the lighter, like all my other gear, is ready to use at any time.

I've had a few cold weather failures with Zippos, but that was due to my fingers being too frozen to crank the striker. Eventually I got it to light, but it was a lot. I doubt I could've done much better with other conventional ignition systems either.