I stayed in Madrid with Moises and Cristina for one month, in October/ 2012, and I had an excellent experience.
They have a beautiful “retro style”, very clean apartment, in Malasaña, with an amazing view.
Malasaña is a trendy, vibrant, “vintage” area of Madrid, with nice shops and restaurants and great nightlife. You can walk to many places because it's near the center of the city, particularly, Plaza de España, Sol, Fuencarral, Gran Via…but if you prefer to use the metro, it’s very close to their house.
The room that I rented was very nice for one or even two persons. My boyfriend stayed with me for one week and he had no problem.
Moyses and Cristina are great hosts, very friendly and helpful , always available to help me! I never felt alone! ;)
They introduced me to “CAVA”, a Spanish drink like “Champagne”, and made me a farewell dinner with a delicious Tortilla made by themselves!

I give them 5 stars because and definitely i'll go back to the Moises's flat when I'll return to Madrid!