Stayed March 2013.
The riad is in a great location 5-10 minutes walk away from Djemaa el-Fna. It's amazing how quiet and relaxing the atmosphere is compared to the main square and busy souks both inside the riad and on the lovely roof terrace. We stayed 2 nights in the Arba room before going to the desert and then 2 nights in the Wahid room. Both rooms were great, but it's worth the extra for the size and comfort of the Arba room! The staff made us feel like part of the family and were very accommodating, always willing to make incredible mint tea, answer any questions we had and get up to make us breakfast at 6am when we had an early start.
The only slight downside was that one of the riad's neighbours was doing some work on the outside of his property just outside for the last 2 days of our stay, which started quite early in the morning. This was obviously no fault of their own and could happen anywhere in such a busy and compact city, but the staff were very apologetic nonetheless.
Would thoroughly recommend Riad Diana to anyone looking at going to Marrakech!