I switched in late September. The real problem with VZW was the poor signal at home, 1 bar - maybe. I knew that AT&T signal was better but could not find a way out of the VZW contract until my son (he really wanted an iPhone) contacted VZW on his account and VZW sent out a tech who rated our VZW cell service as marginal. There is statement in the contract that says if VZW can't service you with a reasonable signal you cant take your number and go, no fees or early termination costs. I had to get VZW to put this info in my account from my son's account and from then on it was no problem. Went to the AT&T store and bought two 3G's - 16GB. Last VZW bill did not include any term fees etc.
When I was buying the iPhones, the AT&T folks said the VZW server that ports the numbers was slow and incoming calls might not work until the next morning (it was 8PM when I bought them). The incoming calls were ok by 9:30P.
All things considered, a reasonable experience.
I have found the 3G network fine in both Eastern Massachusetts and SouthWest Florida.