I stayed in Nuria's apartment for 5 nights.
She received me in person, she is so nice and polite. She gave me all the information I asked her, maps, restaurant recommendations, etc. She left a basket with fruits too.
The apartment is perfectly located in Downtown Madrid, one block from Callao, one of the busiest hubs of la Gran Via. There is one subway station one block away, just be careful: if you come from Barajas Airport with luggage, you need to know that you have to take three trains, and there are too many staircases between connections (without escalators).
The apartment is very new and nice,well equipped with everything you need. There is a Corte Ingles supermarket just one block away, where I bought food and things for breakfast, so I saved a lot.
The decoration is a bit "girlish" (I am a man and was just by myself), with pinkish things everywhere, but it did not bother me at all.
The mattress was very comfortable (it is a double bed, be careful if you are used to Queen or King beds) , Wi-Fi worked fantastic, and she even has an Ipod station so I could listen my music.
Some nights were cold, I put the air heating system and it was warm in just 5 minutes