Getting from Rome to Sorrento

No, not 7 hours. From Roma Termini take the Freccia to Napoli Centrale. 2nd class is absolutely fine on these trains. From Naples you have a couple of choices (maybe, it depends on when you will be traveling). The Circumvesuviana train goes directly to the middle of Sorrento. There's also an express version (Campagna Express) that travels less frequently. OR, if you like the water, take the ferry across the Bay of Naples. It lets you off below the city but you can get up above by bus, elevator or foot.
Scenic and relaxing. directferries.co.uk will show you both options for ferries.

I love Sorrento and spend about a week there every year. No, there isn't much to do but somehow I never get bored with the shopping (love the linen shirts for men), the food (Trattoria da Emilia, Hotel il Nido, Inn Bufalito), the scenery (especially sunsets!!!!), the people and availability of the Amalfi Coast, Pompeii, Capri. ENJOY!

Freccia train Roma Termini to Napoli Centrale is about 75 minutes, then in the same station (I believe downstairs) you can catch the Circumvesuviana train to Sorrento near the center of town. All told you should be able to do it in under 3 hours total.

Yes you do have to change trains but it's not difficult. From Rome's main train station (Termini) you get a direct fast train to Napoli (less than an hour and a half). Once there you go downstairs from the main station to the local train (Circumvesuviana ). It's more like a commuter train. It takes about an hour. The advantage to this rather than the ferry is that you are already in the train station in Naples whereas for the ferry you'd need to get to the ferry terminal which you probably wouldn't want to walk so you'd need a taxi. Then once you arrive in Sorrento you need another taxi to get up to the main part of the town which is situated up on a cliff. The train goes right to the center so if your hotel is close enough you can just walk. Even if you have to wait a few minutes for the next Circumvesuviana train the total time shouldn't be much more than 3 hours.

Not sure where you got 7 hours?

If changing trains does not appeal (it’s quite simple)
You can take fast train to Naples then have a driver pick you up there to take you to Sorrento
Should cost around 95-100 euros

Thanks everyone! I don't know where I read it would take 7 hours! Looking at the map I knew that had to be wrong. Appreciate the restaurant tips also!

In August we went the opposite direction: Sorrento to Rome. Took the Italo high-speed train. 1 hour 10 minutes from Naples.
Together with the Rome-Naples route, Italo has buses between Naples and Sorrento - so one could take Italo for the complete route between Rome and Sorrento.
Though we took the Circumvesuviana train to Naples (to catch the Italo train to Rome), we would have taken the bus if the connecting time to our Italo train had worked better.

Even in May, Sorrento can be very busy. You should book your hotel six months in advance if possible. It is quite likely you will not get your first choice. Note that advance (3 months, I think) Frecciarossa tickets are very cheap, but non-changeable and non-refundable. Price can vary with time of day, too. We were refused permission to board the train before ours when we happened to arrive that early. So we sat on our luggage for an hour, instead of paying the full walk-up price for new tickets.

Make your plans for your departure from Sorrento advance, because the need for multiple public transit "seats" can result in an unpredictably long trip to whatever your next stop might be. I particularly mean a flight home, for instance. I mean, planning out the day in detail, not necessarily ordering a taxi.

I've taken the Circumvesuviana from Naples and it's not for everyone--the trains are crowded, hot (no air-conditioning), and often have pickpockets. If your schedule is flexible, I'd take the Italo train-bus connection to Sorrento or the Campania Express from Naples, which runs on the same tracks as the Circumvesuviana but is less crowded and has air-conditioning.