We stayed at Margutta 54 for three nights in a fairly warm April 2011. We had the Deluxe suite, and our friends were next-door in the Superior suite. These were the two ground floor rooms, and were extremely comfortable and spacious. I would agree with the previous reviewer who said the rooms lacked natural light. The Deluxe room was the darkest, as it's in the corner, but we quickly got used to this. Margutta 54 is in a pleasant courtyard in a built-up area, so you're not going to have much natural light.
The room was very well furnished, the large bed very comfortable and the powerful shower was quite fantastic. Via Margutta is a great little street, and there was an art fair there during our stay. It's a short walk to the Spagna metro station from Margutta 54, and there's a useful bakery/cafe just after you get onto Via Babuino from the bottom end of Via Margutta. We enjoyed a meal at Edy's, which was a couple of minutes' walk from the suites, and drinks at Il Margutta.
As there are only four suites, you shouldn't expect typical hotel service here. Although we had informed the hotel the time we expected to arrive, there was nobody there to meet us, and nowhere indoors for us to wait. We waited outside for about quarter of an hour, after which someone arrived to let us in. You do get free wi-fi, but it only worked in the sitting area of the Deluxe suite. They could do with a booster to increase the signal strength. We were also a little disappointed that we weren't provided with a free bottle of water every day. The room rate is high, and it would be a small and convenient gesture.
On our last morning, it became clear that people had arrived in the room upstairs. There was quite a lot of noise from their stomping around, and voices were clearly audible. So we were relieved that they hadn't been there for the majority of our stay.
On checking out, the butler agreed to take our luggage to our next hotel (as we were staying at Babuino 181, which is owned by the same company), which was very useful.
I've focused on some of the drawbacks, but we really enjoyed our stay here, and were very comfortable indeed. On returning to Rome, we'd consider staying here again, partly because it's such a fantastic area, and partly because the room is so comfortable.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC