My boyfriend and I stayed in the Mondriaan room at the "stay at ours" guesthouse at the end of November.
We really, really enjoyed our stay there; the location was excellent, the people were friendly and helpful, and we felt totally at home there.
As there were some problems getting there from the airport (due to train issue) we had to ring ahead and let them know we would arrive late. Despite this, Frederic stayed up and waited for us to arrive and then spent a long time letting us know where all the best spots were. This was much appreciated.
The next day, we also hired bikes from them. This was a great way to see the city and all of the roads were easy to navigate.
The room itself was comfortable and clean, although you could hear the people in the room above you. In addition, the waterbed was a definite experience not to be forgotten!!!
We had a lovely time in Amsterdam, and would definitely return to this accommodation if we were to go again.