It's not just that it's slow; apps quit where they never did before (ie. safari browsing MR, viewing or deleting emails), it freezes, and it restarts itself.
Same here—I actually have zero complaints about speed. The UI and typing seem faster, if anything.
But memory seems to be completely logammed: apps quit, or take several tries before launching. Even Mail loads slowly now—which means (I believe) that it exited due to low memory. Worst of all: my iPhone spontaneously reboots itself several times a day.
How is Apple letting us down by providing us with a better OS? Fatter software will always require more H.P. [sic] to run correctly. It's the same as running the latest version of Photoshop on a G4.
I think Apple should have probably not have released iOS 4 for this model (the 3G just can’t handle it—way too little RAM). It’s not like your Photoshop analogy: a Photoshop upgrade isn’t automatic and assumed to be OK, and it doesn’t come from the maker of the computer.
At the very least, in hindsight Apple should displayed a warning in iTunes: “An iOS update is available. However, your device has less than the recommended RAM, and may be unstable. Do you wish to upgrade anyway?”
There’s always hope that some patch will make iOS 4 less RAM hungry... but we all hoped for that in vain with iOS 3 slowed down our 3G’s. (Now that WAS a slowdown. iOS 4 seems no slower than iOS 3, but I remember the first few weeks of my iPhone, with iOS 2, when it was actually fast!)
This doesn’t have me overly upset because (a) when the phone’s not rebooting itself, the folders are really cool

And (b) my iPhone 4 is coming soon
But if I was keeping this 3G, I’d be mad at Apple for pushing out this update with no warnings.
Now, maybe our bad experiences are the exception—in which case, they may go away! But I’m not optimistic right now.
I thought the exact same thing!
There has never been so many negative comments about any of the previous versions of the iPhone, as there has been about the iPhone 4. Yes the iPhone 4 is pretty, but it doesn't work as advertised. It was pushed to market way to soon. Imagine what would have happened had Apple waited until it was done right and then release it when they had a firm contract with Verizon. That move would have crushed AT&T!
To be fair, in truth EVERY Apple product for ten years has been met by howls of pain and rage, and cries that Apple has suddenly lost their high quality. This one’s not especially different from many past instances. What IS changing over the years is that Apple’s huge popularity makes them big news. So the media feeds the fire a lot.
I ordered an iPhone 4 despite these “terrible” problems. Yes, in certain situations (where the signal is already bad) you’ll want to hold the phone a certain way or risk losing the call. But the iPhone 4 gets a better signal—and holds on to a call with a weak signal—better than previous phones. Andandtech tested this pretty well. In other words, the “terrible” new antenna design is, despite the known flaw, STILL better than previous antennas.
As for the proxy sensor, that sounds like software. These things happen. Wait a month before buying a new product (from ANY company) and you’re better off.
And another reason you’ve never heard as many complaints about past iPhones: Apple has never SOLD as many as they have of this model. Double your sales, you double your complaints. Go on any product forum for anything from cars to clothing and you’ll think every product is crap. Forums are were people complain and seek help—they’re not a good way to judge the absolute scale of a problem.
But that’s the iPhone 4. Back on topic, I wish my 3G were able to handle iOS 4! At least make some system process (or Mail, or Safari) quit itself more aggressively when in the background, leaving vital RAM for other apps. It wouldn’t be ideal but it would beat all these reboots.
I’m going to try the “double hard reset” later.