Got mine on the 24th, thoughts so far:
Camera is VASTLY better and is now comparable with other decent quality phone cameras in my eyes. I've actually started using it, whereas with the previous ones that was once in a blue moon. The pictures it takes are actually good enough now.
Video camera is great but I do find it has a bit of a wibble to it. Hard to explain, but I see it in everyone's videos. To be fair you see it on other cameras too and if you don't shake it about it actually takes quite good footage - again, I've actually been using it whereas I haven't with previous ones.
Battery life is markedly better, which I'm very pleased about. I'd say the 30% claims are about right.
Screen - Amazing! As more apps update to include retina display graphics the phone gets much nicer to look at. Best phone screen I've ever seen, by miles.
Gyroscope I dismissed as a gimmick but if you try Eliminate: Gun Range, you can see instantly what the implications are for iPhone games, it works really really well and I'm definitely interested in what games developers will do with it.
Antenna - hasn't bothered me once but it's been in a case in day one. Disappointing that it's happened but we'll see if they fix it with software. If they do manage a genuine fix then all is forgiven. Huge oversight on their part though. Ridiculous.
The look of it I'm completely in love with. I liked the 3G/S, but this looks way better. Had a few customers say they don't like it though, too square. I love it. But I am absolutely terrified of dropping it. The band and the glass panels are so rigid that I'm convinced we're going to be seeing a lot more broken iPhone 4s than 3Gs. No flex to it at all and I think they will just.. explode basically. We'll see. I've always kept my iPhones in cases anyway. Buttons feel nicer too, huge improvement over the old ones. Also fits with the style of current Macs, the 3G didn't from day one and I always thought it was a bit strange.
Speed - Definitely a lot snappier. Some of the new games are very impressive. Just feels nicer in general use, got a bit more pep to it.
I'd definitely do the upgrade again. I did, in fairness, get quite a hefty sum for my 3GS which fully paid the early upgrade and the whole thing only cost me £135 of my own money, but it wasn't some special deal, it was just recycling my 3GS + early upgrade
