I'm not a technical photographer of any sort, but I definitely do enjoy taking pictures at every opportunity and editing them to no end on my computer or on the iPhone. That being said, I've seen what the iPhone 4 can do time and time again. It is one of the top competitors in the cellphone camera realm, unquestionably.
That being said, the iPhone 4S camera seems leaps and bounds better to me. Color balance, shutter speed, indoor/low-light sensitivity, and even the speed at which the app opens amazes me. For someone who had become so accustomed to the strengths and weaknesses of the sensor and camera on the iPhone 4, it is amazing to see the differences that come out of the same package. Hell, this is the first time I can digitally zoom with a phone and not want to puke at the results (due to the MP increase). Coupled with quick edit on the photo.app or one of the myriad apps on the App store and you've got yourself one crazy improvement. Not to ride Apple's d, but I like what they've accomplished here.