Yes, constantly. And I find my dad and brother complaining about how slow Netflix is running, and so I always have to help them clear out their multitask.
Having 5 apps open in the background is fine, but then when you have 50 apps paused, and they're all games, that becomes an issue.
Wrong
----------
TrueOnly if an app locks up completely or has some network issue and won't refresh information. Other than that, there's no need.
----------
iPhone 4, yes. iPhone 5, no.
No difference. It's iOS. Not based on phone model.