In Sorrento -

We hired Gennaro from SorrentoLimo.com. He was fantastic. We did the Amalfi Coast (Positano, Amalfi, Ravello) and a quick tour of Sorrento.

In Naxos - Definitely take the ship's shuttle or taxi (approx 20 Euros)to Taormina. It is a lovely town. I just spent a few days in Sicily at the end of May and went back there. Be sure to have granitas at BAM bar and explore the ruins and all the pottery shops on the street leading up to the ruins (Via Teatro Greco). I have bought things at Farano and other places on this street on my last two visits.

In Santorini - We took the funicular up to the town of Fira and then found the taxi station just off the main street. We hired a taxi to Oia (about 12-15 Euros) and then took the bus back. Very easy to do on your own.