I've been a long term BlackBerry user but decided to try the new iphone during my recent Vodafone "upgrade", going to the iphone 5S, which I got from the White City London Vodafone store mid-December.
To date I bitterly regret it. I've now had four 5s phones, three from Vodafone and one from Apple and the finger recognition hasn't worked reliably on any of them. They all do exactly the same - after setting it up it works pretty much flawlessly for a day or so but then degrades. I've tried all the tricks, including resetting, redoing the finger scan, scanning the same finger (my thumb) several times and nothing settles it - once reset it works for a day or two but then degrades.
I'm now due to get my fifth replacement on Monday. I'd really like to go back to a BlackBerry but Vodafone won't let me, which is really annoying because as far as I can see the 5s isn't of merchantable quality as they simply don't work as advertised - and the finger recognition was the main selling point for me. Not a good intro to Apple.
What I find unbelievable is that from my conversations with Apple personnel none of them have heard of the problem before, which must be a lie. From what I read on the internet it seems like perhaps 25% of the 5s phones issued have this problem (whatever the problem is), which, if the case, clearly means Apple must be well aware and are trying to keep a lid on the fact that their new flagship phone doesn't work and shouldn't have been issued - yet anyway.