I don't see any reason (as of now) to go back to Verizon. My main concerns were internet and 3G quality after reading so many horror stories about no internet for hours at a time, etc. But in all honesty, I would take AT&T's EDGE on a much prettier and responsive iPhone than Verizon's largest 3G network on an LG envTouch's pixelated and awful screen. Even if I switched to a Droid, I can't imagine having better internet quality.
And with all these rumors for Verizon to offer the iPhone and whathaveyou, that, to me, only means that AT&T's bandwidth would be freed up and Verizon will have a taste of shutdown networks and slowed service. And LTE is just around the corner- so we'll be sharing service off each others' towers essentially. So then what?