My family (2 adults, 2 teenagers) stayed at Residenza Domizia for four nights at the end of August, 2009. I originally tried to book the hotel through Orbitz, but the customer service person took so long to finish my order that they didn't have 2 doubles left at the price I wanted. So, I took a risk and emailed the hotel directly, using the email address on the website. The very next morning, I had a response and they confirmed 2 doubles, each for 100 euros a night, with a full refund for cancellation up to 24 hours before check-in. I then emailed with them at least 8 or 9 times in the weeks leading up to the trip. I asked about everything from their smoking policy (all rooms are smoke-free) to what cleaning chemicals they use (unscented) and got prompt and helpful replies. They offer a private car pickup at the airport, but it's much more expensive, so we just took a cab (don't pay more than 40 euros). We arrived a little early, but were able to check in at 40 Coronari by 8:30 am on a Saturday. You need to ring the doorbell (push, don't pull the door) and go up one flight of stairs to check in (there's a little sign next to the door). The guy who checked us in was a little gruff and didn't speak much English, but he ended up being very helpful later on.
Our rooms were in 236, right down the street and were both directly off the breakfast room on the second floor. One of them (Via Margutta) was quite a bit nicer than the other (Via Frattina) and had a little hallway and spacious room with a high ceiling. That was the room I stayed in. There were plenty of windows, a desk, clean bed, etc. The shower and bathroom were fine, and had a nice towel-warming rack. You need to place the towels on the floor to have them changed, and place the laminated placard on the bed for linen changes. There's a flatscreen TV, but we only got channels in German, and didn't really have time for it anyway, so we didn't bother to figure out how it works. The air conditioning and ceiling fan both worked (although the fan was unplugged, so but one of the staff came and plugged it in for us) and the room was extremely cool in the day and at night.
Internet: If you're from the US, you need a plug adapter for your computer or other electronics. I didn't bring one, but the guy at the front desk had one and lent it to me. He also lent me an ethernet cable for the hotel in the room, which was fast and reliable. Apparently, they also have password-protected wireless, but I didn't find that out until the last day. Minifridge was under the window seat, but items cost money. We just used it to store food. Our view wasn't that great (basically an alley, but the light from the window was lovely).
Even though we were next to the breakfast room, it was NOT loud. We were the only Americans I saw the whole time I was there, and everyone eating was extremely quiet and polite in the morning. I LOVED the breakfast. They had yogurt, cereal, croissants, coffee and juice, crackers, jam, etc. It was delicious and probably had a value of about 15 Euros, especially considering all four people in our family ate there every morning. It was served from 8-9:30 am, which gave us plenty of time to eat before heading out. The front desk will call a cab for you if you need to go somewhere, but I think there's an extra charge and they run the meter while they're waiting, so it's better to go to the cab stand next to the Piazza Navona, which is right down the street.
Location: AMAZING. It's about 5 minutes from the Vatican gates and the Tiber River, a block from the Piazza Navona and tons of shops and delicious restaurants (avoid the ones in the Piazza, because they're way more expensive than the restaurants a few blocks away). I walked to the Trevi Fountain (10-15 minutes) three times while I was there. It's about 10 minutes to the Pantheon, and the Colosseum and Jewish Quarter are also walkable distances (although longer in the heat). The streets are beautiful and ancient. It's as close to everything as you can possibly be, and there's always something to do and look at. I highly recommend this if you like to wander around in the evening (the area seemed very safe and we had no trouble with pickpockets) or don't like paying for a cab or bus everywhere.
An unrelated warning: DO NOT change money at the Western Union or other "Change" places on the street. Go to a BANK only. Those places will charge you a "transaction fee" of as much as 18% of your money. Get euros before you go, or use a credit card or traveler's checks. They will rip you off more than any pickpocket, and without apologies.
I recommend this hotel. It was pleasant, clean, good for people with allergies (hardwood floors) and the breakfast was delicious. Location can't be beat. My only complaint would be that the main staff member we dealt with was a little hard to communicate with and one of our rooms was a little small, but otherwise it was lovely. I think negative reviews here are often due to the fact that people with good experiences may not write in, or people have unrealistic expectations of what a hotel in this price range should be like.
I've attached photos of one of our rooms, as well as the breakfast room and street.
Enjoy Roma!