Apple have released some real sample pictures which have been taken with the iPhone 5. They say these photos are completely untouched, except from being resized.
There doesn't seem to be any huge improvement over the iPhone 4S. Apple did state that the camera was better in low-light but they don't seem to have any low-light examples so I don't think it'll be that great in low-light.
However we can no way expect a phone to compare to your DSLR or Micro Four Thirds camera because obviously the sensor in a phone is a lot smaller.