Me and my sister stayed at the Dar Limoun in March 2011 and had a lovely time. The Dar Limoun is clean, comfortable, and is very central, only taking a few minutes to walk to the square and the souks. We went on two trips whilst staying in Marrakesh, one to Essaouira which was lovely, and Ouarzazate another day, which was lovely, but it's a long, long way to travel and no good for people who don't travel well!

We stayed here twice, at the beginning and end of a ten day stay in Morocco. Typical small Riad with rooms around a courtyard, a sunny roof top terrace and friendly and helpful staff. The room was clean and tidy and though the shower room was in need of a bit of "refreshment" it also was clean and worked well-lots of hot water and fresh towels each day.
By no means a luxury destination but fabulous value with a decent breakfast included and,of course, a brilliant location literally two minutes from the Djemm el Fna which is where you want to be in Marrakech.
Will I stay here again? Certainly

Stayed here for 5 nights. Excellent location, literally 2 minutes from Jemaa el Fna. Hard to find the first time - turn left just before second overhead stop sign on Dar Zitoun (if heading away from Jemaa el Fna), failing that ask someone but be prepared to pay for their assitance.
The hotel itself is simple but very pretty. The rooms are basic but have everything you need, as with the bathroom. I imagine the rooms are good in summer as they were very cool.
There is a courtyard with seating and an excellent little roof terrace to relax on in the day or night with a table, chairs and cushions.
Breakfast is provided in the morning which we were not expecting and the staff are very welcoming and helpful but generally leave you to get on with it.
The manager Fouad was kind and relaxed and didn't seem bothered when we arrived home pretty late a couple of nights.
We went to a couple of other Riads of friends we met, and Riad Zitoun definately seemed the nicest.

There are many fancier, plush (and less Moroccan) places to stay for more money, but Dar Limoun really is close to Djemaa El Fna, is comfortable, super clean, has great staff, has proper bathrooms and cost us ~$40/night for a double B&B. We were pleased with the choice!

Although difficult to find the first couple of times (like everything in any Moroccan medina), it was an island of peace and serenity. The week we were there, the temperatures topped out over 50degC (that's in excess of 120degF), but we were still very comfortable with only a small tabletop fan in our room. The caretaker is very friendly and takes his job very seriously - he let us in and showed us our room, allowing us a shower and a 2 hour nap before we found him to fill out the mandatory forms and pay him for our stay. Once you learn your way around a bit, Djemaa El Fna is less than 5 minutes walk and the alley back the Dar Limoun is easily found in one of the corners leading out of the square.