I spend three weeks at Javier and Julia's flat — for professional reasons, and also to discover a new city —, and everything was great ! I highly recommend !
When I arrived, Julia was there to meet me : she is very nice and careful. She explained me everything I needed to know about the flat, and the neighborhood — good restaurants, what I had to see, to visit, where to go shopping. She left me her phone number, telling me I could contact her whenever I'd want or need.
The flat was pretty nice : really cosy, well endowed, clean, bright, spacious. It has been really enjoyable to live in, even such a time. When I was alone, it was of course perfect. But it was also perfectly suitable when my friends came to visit me some days. Even though the apartment is at the heart of Madrid, in a street that can be very busy (for the week-end), it is very quiet, by day as well as night : I had no difficulty neither to work all day long, nor to sleep (even the week-end).
The location is perfect : I used no public transport the all time I spent in Madrid (except to come from the airport, of course !). Every nice place of the downtown — Puerta del Sol, Plaza Mayor, Palacio Real, Parque del Retiro, even Casa de Campo, Museo del Prado —, and almost all borough of the city center are easy to reach on foot — Malasaña, Chueca, Letras, Sol, Latina, Austrias. The flat is near to very nice restaurants, and is very well-located to party also !
In short, I spent three great weeks at Javier and Julia's flat — thank you so much to both of you ! —, I highly recommend this place, and I hope I'll be able to come back as soon as possible !