As for the GPS, while I've only had the phone for 36 hours, the few times I've played with the Maps app and other GPS-enabled apps (like Bing maps, which I find to be more up-to-date - Bing has an arial view of my house while Google Maps arial views are from before the entire neighborhood existed) seem just as accurate as the AT&T version of the iPhone 4.
But I will put it through its paces tomorrow with Navigon to see how it does since the OP brought up his concern.
Finally, thank you. Of the last 20 something posts, all I see are bunch of speculations and most of them probably don't even have a Verizon iPhone just yet? This is GPS problem, YES the "ATT vs. Verizon data speed issue" MIGHT have something to do with it but the OP stated that the GPS actually loses signals, that has nothing to do with data speed.
But instead of shut up and just test the GPS yourself or wait for other people to test the GPS for us, most of you just can't help but to point the finger at the data speed issue? Come on people, we all know there is some sort of data speed issue, but let's be reasonable here.