I'll just say that there are both upsides and downsides to Verizon. Let's hope, at least in terms of the iPhone, that there are more upsides than downsides.
The one downside that sticks out at me right now is that this is a CDMA phone, not LTE 4G, so simultaneous voice-and-data like with AT&T is impossible with Verizon. That means while you're using the new wi-fi hotspot feature (a very big upside!), you cannot make or receive phone calls. Whether that means the phone won't ring or your wi-fi hotspot just disappears remains to be seen.
Be sure to report back and let us know your experience -- I am VERY curious about it (even though I have no big gripes about staying with AT&T).