In May, we used Raffaele Monetti of Monetti Taxi, and had a great experience. He is listed in the Rick Steves book. (http://www.monettitaxi17.it/English.htm) We were staying in Sorrento and booked a trip along the coast and down to Paestum to see the Greek temple ruins. Raffaele picked us up, and stopped at scenic spots along the coast. After our stop in Positano, I mentioned that I wanted to go to Ravello on another day by bus. Raffaele adapted our tour to include that. (We saved Amalfi town for another day since it was easier to get there by bus.) That worked out great for us, and then we were on our way to Paestum. My husband was delighted to see the temples at Paestum, but it does make for a long day since Paestum is about 2 hours south of Amalfi. A private driver is not cheap, but the experience was worth it to us.
We were there early May, and started at 8:00 AM, so there roads weren't too crowded, but even so, my husband, who loves to drive, commented that he was glad he didn't attempt the drive. Those who drive it all the time know to anticipate the curves and bends where oncoming vehicles will be in your lane, and know just how much space they need to squeeze by in the narrow towns.