A very good idea by Greg Kumparak on TechCrunch:
Here’s the dream: one lock-screen, two PINs. One for me, one for anyone else who might use my phone but doesn’t necessarily need to see everything.
Not only is it a good idea for there to be a guest mode, the implementation is quite nice and simple. Maps, Phone, Clock, Calculator, Safari. Perhaps the ability to granularity add/remove from that default set. Everything is stateless and rest when guest mode ends.
This could potentially even lower the divorce rate in the US.