My fiancee and I both have droids. We drove from NJ to Bradenton FL last week and relied solely on our Droids to get us there and back. I'll admit I was a little weary about this at first, so I did have paper directions sitting in the console but I shouldn't have wasted the time or trees.
Before leaving I created a google map of all of the destinations we needed to hit. Then I shared w/ my finacee so either of us could quickly bring up the map, press the destination and nav to it. This worked very well.
The nav was awesome. To anyone that doesn't know, in that area of Florida just about every street is named via number. There is no way we would have made it around town (the place we were staying, the bride's house, rehearsal, church, reception.....blah blah) with paper directions. The droid rocked for local nav.
On the highway it was also pretty good. It did route us to a few odd highways around the larger cities (DC, Baltimore) which I'm sure would have cut off a few miles but not sure they would have saved us any time. The nice thing about having a second droid in the car was the ability for the co-pilot to take a look and decide wheter or not to take the odd route. The droid re-routes you very quickly when you decide to ignore it.
Both times through DC the phone tried to send us on the western side of the beltway which was backed up with traffic both times (which the phone was aware of, since the red light next to the ETA was lit). A nice feature would be auto-routing around traffic. There are more than enough freeway options around DC to skip out on traffic. At least a popup that says alternate route available + 2 miles or something to that effect. Another plus for having the second droid is the ability to check traffic way ahead of where you are via google maps.
The co-pilot was also able to check ahead and plan stops accordingly based on food/starbucks availability which worked out very well. We ate chic-fil-a about 5 times because the chicken nuggets are good and easy to eat while driving, so searching via maps was a big help here.
95 was closed in NC on the way home so finding our own detour was super easy. Using traffic we estimated where to get off the highway. It was a pretty sketchy area too, so I'm glad we weren't putzing around at night. I spotted the alternate route right away and used my blue location dot to guide me through it by eye, since nav would have taken me right back onto 95 where we got off. I did eventually hit the nav once we got close to the higway again so I didn't have to keep watching the map.
We planned for an overnight stop on the way down in VA, so we knew where the hotel was. On the way home (didn't get started until 11am) we decided we needed to stop at about 10pm. Again, using maps it was easy to locate hotels that were 1, 2, and 3 hours north (we started this about 6pm) and call ahead to get the rate.
The phones were ridiculously useful. Having the second droid made it so much easier, even though one person with 1 droid could have done all of the same if they stopped (don't think you can do all of that safely while trying to drive a car).