The best camera is the one you have with you, so I carry a very nice point-and-shoot everywhere. Nothing else has been good enough. But the iPhone 4 is.
Five megapixels is good enough. Photos are "real camera" size. I've always wanted a point-and-shoot camera that's frozen at 5 or 6 megapixels, with the quality of the pixels boosted every year. I kind of hope the iPhone does this. The Droid X, the new "platinum" Android phone according to Google's Andy Rubin, does not take better photos by any stretch of the eyeball, even though they are bigger, at 8 megapixels.
I take pictures mostly of friends and food. (Sometimes together.) You can almost feel the texture of a lemon rind, the gloss of oil on noodles, the veins on a leaf, the freckles on someone's face or the little creases in their teeth. It's nearly the kind of fidelity I expect from a quality point-and-shoot. Looking at the result a split second later on this phone's screen? Surreal.
The colors pop. Pleasantly, but almost unnaturally, super saturated and contrasty, the kind of processing I love in Nikons, taken to the extreme. That's the iPhone 4's secret sauce. Color and contrast. Apple's not going for accuracy, they're going for your eyeballs. Look at the fruit captured by the iPhone compared to the S90—the latter's photo is far more natural, but I want to make lemonade with the lemons in the iPhone's photo. When I touch up photos, manually, that's about what I do to them anyway.
Maybe the other camera manufacturers should do a bit of it too, like in our enhanced taco photo from the Evo. At first glance, most would say the Evo takes worse shots. After boosting the contrast in Photoshop? It looks even better than the lofty iPhone 4 (in this shot, at least).
Dimly lit bars, that smell like must and old beer, or hair-gel-heavy nightclubs. That's where most people (intentionally) take flash photos. The iPhone 4 won't produce the kind of dreamy night portraits the S90 can. The flash is strong, but aesthetically, what comes out looks like any other phone—washed out, blown out—just warmer, and less grainy. I would leave it off.
Warmth is also what you notice about the iPhone 4's photos and video in low light. They're richer, fuller. There's color and more of a sense of life in the photos, more like a real camera.
The sensor's pixels do pick up more light than the average phone camera. (And Apple clearly cranks the noise suppression too, just enough.) That's partly because the lens is faster, and wider. The iPhone 3GS and the Droid X's have f2.8 lenses that cut closer photos. The iPhone 4 has an f2.4 lens, so it lets in more light to begin with. I prefer the wider view, too. The kinds of things I take pictures of with a phone, I'd rather shoot wide, not tight.
720p video is good enough. It's HD. The iPhone 4's 30fps framerate is smoother and more consistent than the Droid X; the colors more vibrant than it or the Flip. At night, the iPhone 4's video looks more natural, and less washed out. It has the same problems as other cheap camcorders, of course, like the jelly effect, and nonexistent stabilization. On the other hand, there's no reason to carry a separate cheap camcorder ever again.
The front-facing 640x480 camera isn't very good, but it isn't disappointing, if you don't have high expectations. I didn't. It's a much tighter lens than the back camera, explicitly designed to frame your face during a call, and not much else. I would stick with decent lighting for FaceTime calls. (The Evo's front-facing camera is better, FWIW.)
It's fast too. Instant. Seriously, the speed at which it reacts to your touch is jarring in the most feel-good of ways. The only other phone camera I've used that's nearly that fast is the Evo. It's easy to get to everything. Tap to focus. Tap to switch cameras. Sometimes I wish the iPhone 4's camera had more extensive controls, like a few Android phones, because it takes excellent enough photos to make me want to fine-tune them. But I also like not thinking about it. Touch and shoot. If only you could use the home button as a hard shortcut too.
Of course, the $400 S90 takes better photos. It's a miraculous little camera. But consider just how narrow the gap is between it and the iPhone 4 (the cellphone shooting challenge this week should be interesting). The iPhone is always in your pocket. I have to pull my S90 or DSLR out of a bag, wasting seconds—an eternity and a half when you're trying to capture a moment.
I'll keep my S90 in my bag. But I don't know often I'm going to pull it out anymore.