We stayed here in May 2009 based on nothing more than the reviews on Tripadvisor and once again I wasn't disappointed.
As others have said this hotel is clean, quiet and well-located.
The rooms aren't big but very nice and spotlesslessly clean. It appears that the place was either fairly recently renovated or very well upkept or both.
The location was excellent as far as we were concerned. Its a bit of a walk to the touristy stuff (colleseum, Trevi, etc.) but no big deal. We would walk to all the sights and at the end of the day if we ended up too far from the hotel we would just take an relatively inexpensive cab ride back. The immediate neighborhood is great. Abour a million reasonably priced and tasty restaurants within a 15 minute radius of the hotel. Lots of interesting shops as well. Less touristy than other parts of the city.
The courtyard surrounded by orange trees was ideal for relaxing after a long day of sightseeing. Breakfast was basic but good and the service excellent. Afternoon snack was also nice though we weren't always able to take advantage of it.
The desk people were always helpful in booking tours, recommending restaurants or just giving some general advice.
The only downside I can think of is the churchbells at the Santa Maria go all night every 15 minutes. But I'm a light sleeper and it didn't really bother me.
Also, it can be difficult to find as its on a tiny street hidden among other tiny streets in Trastevere. We just told the cab drivers to drop us off at the Piazza Santa Maria and we walked the last two minutes back to the hotel. That's the only cons I can think of about this hotel.
Of the four hotels we stayed at all over Italy this was my favorite and I wouldn't hesitate to stay here agin or recommend to family and friends.