If you already have an Iphone 4, then this upgrade is very very hard to justify.
Only thing I see on the iPhone 4S that I like is Siri.
The rest is blah blah.
I am going to think think and think.
They're playing the long game here, which is the smart one. All of the people who DON"T have an iPhone or have a 3GS have a compelling reason to upgrade. All of the people who have an iphone 4 won't feel bad about not being able to upgrade right now.
Many people don't like the idea or wouldn't like to early upgrade or cancel their contract, so this gives everybody "something". To us tech enthusiasts, it sucks, because we want the best, all of the time.
For the average person though, I talked about it with multiple college students (student here obviously) through casual conversation and they aren't really interested (just a general vibe I get from people).
Next year, when the largest install base (iPhone 4) can upgrade, the 5 will be big. Plus, the technology isn't really here yet; aside from what they did internally, what else is out? Nothing.
A new screen/design is the ONLY thing they pretty much left out, which is still up in the air depending on who you talk to.