Returning my 4s 64GB tomorrow.
Came from a jailbroke 4/32GB, on iOS4.3.3.
Major reason is battery life, which is simply shocking compared to the 4. Dont know why I should disable loads of stuff to get better life, I upgraded to get most of that extra stuff.
Camera is of course, superb, and I have loved being able to put more music and videos on the 64Gb device. But the effective upgrade price will be £400 (would be selling 4/32GB for ~£300 I guess, both phones bought Apple-Sim free) is simply not worth it FOR ME.... I dont really use the phone for non-productive stuff, and a direct comparison on opening apps, camera, messages, phone apps, well, yes the 4s is more nippy, but again, we are talking maybe 1/2 second here... ok, maybe a whole second with the camera.
Also, very disappointed with Siri. Fun at first, but the more I have used it the more limited I have found it, especially since location related stuff does not work outside of UK.
And I miss some JB stuff, lock-screen calendar.
So maybe for me, all software related, which I am sure will all be resolved in a few weeks or months, but right now, that software is still too bleeding edge.