We had a wonderful time staying at Dar Sbihi. The rooms are small but very comfortable, clean, and characteristic of a true Riad. Breakfast was provided on the roof in the mornings, which was a great start to the day. Sybille (the owner) was incredibly helpful with her advice on places to go both within Marrakech and in the surrounding area. The evening we arrived, she sat us down for tea, went over a map of the medina with us first thing, and then left us to the quintet of Moroccan musicians who happened to be staying there as well. It's amazing that the place was available on such short notice. We were even able to stay one extra day, which we spent going to the Berber Market a half hour outside of town.
Words of wisdom--the location of the Riad on maps we found online was not correct, and apparently they know this and simply haven't had luck getting it changed. So don't rely on that alone to get you there.
Also, under no circumstances should you try to drive into the medina, especially in the evenings, as the major throughfares are filled with people and the smaller streets are too narrow to drive through comfortably (plus, the medina is a very confusing place at first). My recommendation would be to park outside the medina, get a taxi as far in as they can go, and then walk the rest of the way. It's unfortunate but works pretty well.