I've used Nokia Maps in the past a lot for car navigation with my N95 so obviously it is a must work application on the N97 as well. So when I recently drove from southern Germany to Vienna I used the N97 to guide me. While a beta of Nokia maps 3 is already available for some time now, I preferred using the installed Nokia maps 2 to test the stability of the N97. No issues, the GPS works well, a first fix only takes a couple of seconds due to A-GPS support and the route planning and execution works flawlessly. Great!
I like listening to podcasts while I'm driving and in the past this has always been an issue as the built in speakers of my N95 aren't loud enough to overcome the background noise while driving. The N97 has an FM transmitter to send the audio signal to a radio which could be a great solution to the problem.
In practice it's a bit difficult to use as the transmission power seems to be very low. To make the radio detect it I had to hold it very close to the radio. Once detected, the N97 can be removed a bit and the audio signal is still o.k. for an audio (voice) podcast. For music however, there's a bit too much static. I changed the length of the external car antenna a bit which improved the sound quality a bit but still, there is some static in the background. While driving I lost the signal after an hour or so, probably because a radio station came into range which used a nearby frequency. While driving, it's impossible to re-tune the FM transmitter and radio due to the proximity required for the radio to find the N97. This makes the whole thing a bit impractical.
So if possible from a technical and regulatory point of view, the FM transmitter should have a higher power output, the current level is just too low.