Once you are on the island of Corfu, it is fairly easy to do a day trip to the Greek mainland by ferry. But if you are in a hurry and intend to visit both Paxos and Parga on the same day, then things might get a little bit more complicated, as the ferry connections from Corfu only takes you either to Igoumenitsa on the mainland, or to the island of Paxos south of Corfu, but not to both at the same time. In other words, there are no direct ferry links between Paxos and Parga, and the only way to visit both places on the same day is to join a pre-arranged boat excursion organized by one of the local tour operators.
As it turned out, in 2011 such a Parga+Paxos tour runs only once a week, on Sunday. Since I was on the island of Corfu for one week only, I immediately booked an excursion to both places on the coming Sunday. If you book the tour at any travel agency in one of the island's tourist resorts or from the tour rep, the price of the boat excursion would include a complimentary shuttle service from an appointed pick-up place near your hotel to the harbour and back.