Just received my iPhone 4s and couldn't be happier. This thing is AMAZING.
My wife upgraded from the 3gs, I upgraded from the 4. There's a good bit of difference between the 4 and the 4s. I'm not going to waste time going over all the features, since you can pretty much get that from anywhere, but what I will say is that I was really surprised by how good the SPEAKER sounds! I actually sorta turned it on by accident, just screwing around with SIRI, asking it to play a certain song. It did, and it started coming out the speakers, and I was like, oh, that's neat. But then I started to listen, and I was like, damn, that's a seriously high level of detail retrieval and nuance for a - what, 3mm speaker?! I sat it on the shelf and turned it up to 80% and was really, really surprised that it was listenable. I mean, no one's going to mistake it for the JH-13, but for the electronica tune I had on, it was actually perfectly acceptable.
Haven't tested the dac yet, so will post impressions vs the iPhone 4 here when I have. I imagine they'll be identical, or nearly so. But Siri is awesome.