Between its 8MP sensor and internet connectivity, the iPhone 4S is one of the best point-and-shoot cameras around. It can download thousands of photo-editing apps and upload images to a number of services.
But the lack of interchangeable lenses, a weak flash, and other missing features means that the iPhone won't be replacing your DSLR anytime soon. Unless, of course, you had something like the 3RDi camera kit...