Here's another point you might consider. Yes, I've heard that Verizon's network is superior to ATT',s, but I've also heard that this greatly depends upon your geographical location.
Setting that aside, you also have to factor in how many people are going to jump ship from ATT to Verizon. Verizon may experience a massive influx of network usage, while ATT as they hopefully are trying to restore their trunk lines, might wind up leveling out and having just as good or better service than Verizon. The effects of the transition might not be seen immediately, but could rear its head several months after the initial dust settles.
(thanks to Filow for that idea)
On a side note, I wonder when Verizon is going to ditch CDMA technology, given that the rest of the world is using GSM? This also has to be factored in at some point I think, considering that Apple will have to spend more money in order to support the hardware for said CDMA chips. This also brings up whether or not you'd be able to travel internationally with your Verizon iPhone, unless they also put a GSM sim slot in for such use, as they do on some Blackberries.
Doug