Just got myself an iPhone 4S after lining up in front of Apple Store Shinsaibashi Osaka for a tiring 15 hours!
But the iPhone is really worth the waiting! What I really like from iPhone 4S so far is Siri and the iTunes wifi sync.
I bet you have read about Siri's hilarious responses from the net. I can tell you that it's really good and funny!
There's something that you can only do via Siri, or at least I haven't found the way to do it manually by finger. It's the ability to add connections to your own contact info. For example, you can add another contact as your spouse. It's very easy. Just tell Siri to call, for example your wife. If you haven't set it up, Siri will ask you her name as you can see from the screenshots. Pretty cool!
BONUS: Do you know that you can tell Siri to call you by another name? Or by anything you want her to call you :D