I found that when my Droid RAZR gets quite hot when I use it on a trip for navigation. This is nothing new. My original Droid had the same issue. I have found a solution which works for me. It might help someone else, so I am posting my solution here.
First, my car is a 2009 Ford Escape. It has a convenient place for sticking the disk for mounting the unit. That is above the air vents, in front of the center display. This provides for great visibility, but not so great cooling. I decided that if I could divert some of the air from the vent to have it blow on the Droid RAZR, it would work. I made a prototype from a plastic bottle, and found that the idea would work. Then I thought of what I could use to make a more permanent solution. In my case, I had some extra vinyl rain gutter material sitting in the utility room. A section of that was what I used. It was heavy enough to not blow out of the vent yet light enough to be easily worked with the tools I had on hand (saw, Dremel tool and accessories, sandpaper and block). Here's the results:
Top view shows that it successfully diverts air upward toward the phone when it is in the mount. Since it sits in the top slot of the vents, it allows for sufficient ventilation to keep us cool also.
I realize that this solution will only work for those situations in which there is a suitable location for the mount and vents of the right shape and placement to be used. What solutions have others used to help keep the Droids from overheating when being used for navigation? It would be interesting to see what creative solutions others have found.