Seems really nice. I don't know if anyone else has noticed but on my 4S all apps seem to launch much faster, it seems like in half the time they did under iOS 5.
Maybe it's just a fresh OS install or something, but for example the Weather channel app comes on in about a second or two. Angry Birds Rio definitely launches faster.
I believe that real world experience is a better judge of speed and a fresh install of the OS can make a huge difference. I am about ready to activate the new phone. I was making one of my famous hot water fudge cakes and doing laundry so I saved the activation for later.
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I am right 97% of the time. The other 4% doesn't matter.