We had a great stay at Carlos's place. It's a nice accessory flat to a beautiful old house which he's restoring. It's small, but very well thought out, and in a good location: very quiet but a short walk from many restaurants and tourist attractions.
We did find it very cold in the mornings, but I think we were in Mexico City in an exceptionally cold week.
Carlos is a great host, communicative and helpful, and if you stay here you should _definitely_ follow some of his restaurant recommendations. The three best meals we had--in a city where all the food is good--were the places we went to because Carlos had included them in his list of suggestions.