iTried the S3 today, really loved the Widgets/customization options, just being able to add a little widget to quickly adjust the screen brightness made my life a little easier today.
BUT, I can't get over the screen resolution coming from the 4S and having an iPad3. Additionally, the camera quality is TERRIBBBLE. One thing I appreciate with my 4S is being able to take a great pic, touch it up with an app and post it. I couldn't even get the S3 to focus properly on an overhead light in my apartment.
Taking it back tomorrow, hoping the new iPhone is slightly bigger and maybe some customization options

Lastly, I got AT&T to give me a $36 credit on my bill before I even went to the store to buy phone towards activation fee and a $35 credit to cover the restocking fee! All you have to do it ask!