Yes, you can upgrade to iOS 5 right now, click here to learn how.
The assistant feature on the 4s is pretty awesome, but other than that some better hardware and camera is about all that is new. Which is probably why I'm not rushing out to make sure I have it pre-ordered right now. Also everyone is switching to Verizon but even when I do switch, I will stick with AT&T. They offer a few minor features that I found I have actually used that Verizon doesn't offer. Such as the browse the web while you talk feature.
I'm sure at some point I will snag the 4s, unless the iPhone 5 rumors start to swirl before that.
The iPhone 4s is Now Available