Mine (4S) doesn't wiggle in the slightest (and it's almost two years old).
I wouldn't say it rattles unless you shake it, but it is definitely "loose" in the sense that I can move it front and back slightly. Not a big deal though, but I'm wondering if this is something that a lot of iPhones out of the box have. I don't feel like driving to my nearest Apple store (an hour away) for a power button which I'll keep a case on and works/has a perfect screen.