I had the pleasure of visiting Ponza in June 2006 to visit the island home from where my grandfather came from. It is a beautiful place, it caters to tourists, although probably more Italian, as there is little english spoken on the island, but you will get by, and i can tell you where to go if you want some english conversation. If i was to compare it to another island, when we got to Mikanos we thought it was very much like Ponza, although i thought Ponza was a lot cleaner.
Ponza reminds me of many years ago, there are children playing in the streets, laughing and playing, not stuck behind a computer playing games or watching videos. It is a very relaxing island. Only about 45 mins by ferry from Formia (which you can get to by train between Naples and Rome).
The beach that most people go to is easily reached by a shuttle boat for about 3 Euro return per person. Best to take food with you to the beach, we grabbed some food from the dairy right near where the boat leaves from and a slice of pizza (for about 2 euro!) as the bar / cafe on the beach can be expensive but well worth it, they have salads etc there..
If you feel the need to go for a hike, try and climb to the top of the mountain, give yourself a couple of hours and take water with you!!
You can also hire a boat to tour around the island, they are definitely not speed boats, but you don't need one, the sites are just amazing, and the water is crystal clear, make sure you put your anchor down for a few hours of rest and relaxation.