I refered to this forum in making my plans to travel in the D.R. I am really glad that I was not scared away from driving by all the entries warning against it! Driving in general was fine. We found the roads very good, and having a car allowed us to explore on our own and find some very cool and friendly spots. We rented a car from Hertz at the Las Americas airport and drove to Las Terrenas on the Samana penninsula. The only difficulty we had was finding the highway that crosses the island from Santo Domingo to Samana. After several passes, we finally found it. DO NOT get on the "expressway" road leaving the airport. You have to be on what I would call the service road that runs alongside the expressway. Heading towards Santo Domingo very shortly after leaving the airport you will see a toll gate on the expressway, but you will not have to pay the toll because you are on the service road. Almost immediately look for a small green sign the says "Samana" on the right. Once you are on that road you are golden! There is a big, new, bright gas station shortly after getting on the highway that has the best smoked ribs I've ever eaten. We drove to Coson, near Las Terrenas after dark (since we lost so much time getting lost) without incident. Be advised, you need about 1000 pesos in tolls to get all the way to Samana.
We also drove the local roads around Samana without problem. The roads are all in pretty good shape and the main road is beautiful and modern. There seem to be a million motorcycles zooming everywhere, so you have to pay close attention to them as well as the trucks passing around the curves at high speed. It just makes it more exciting!!