Ars Technica joins the discussion with this in-depth exploration, complete with comparison pics:
[P]hotographers accustomed to DSLR quality won’t be trading their higher-end gear for a smartphone camera of any kind, iPhone 4S or not.
In the end, the iPhone 4S offers convenience—light weight, fits in pocket, simple controls—along with competitive, if not excellent, image quality. Unless you need or want full manual control or greater versatility in lens options, the iPhone 4S certainly makes a great photographic tool.