The camera on the iPhone 4S is the best I have ever used on a mobile device.
I no longer need to bring an actual camera anywhere I go outside of a dSLR for specific purposes. The ability to use the "volume up" button as a shutter button now saves you from hunting around for the on-screen shutter button, and new features like grid lines help with shot composition.
It's amazing in low-light situations. With the new camera button on the lock screen, combined with the speed of the 4S and optics, you can take a photo less than 4 seconds after getting your phone out of your pocket -- you won't ever miss a shot again. Photos can now be taken in rapid succession, and the software allows you to edit photos right on the device itself, including red-eye removal, cropping, and an auto-enhance feature.
The video camera is almost as impressive. Finally, you're able to capture full 1080p HD video right from your iPhone, and thanks to the gyro built into the device (it can sense the device's orientation and position on three different axes), captured video is automatically stabilized as it's taken, eliminating almost all shakes. The same noise cancellation techniques that the phone uses for voice calling and for interacting with Siri ensures that the audio taken with videos is almost always crisp and clear.
