We stayed at Juan Carlos' place for 7 days. The apartment is clean and location is great - very convenient, close to metro station, walking distance to central areas and at the same time - in a quiet neighborhood. The apartment isn't big, but definitely bigger than many other offers in central area, big enough for a couple to have comfortable stay. Internet (WiFi) is perfect - stable and very fast. There are several supermarkets nearby with everything you may need. I'd recommend you take a walk in the morning and return by metro in the evening, when you're tired. The closest metro station Strasbourg - Saint-Denis connects you directly to lots of places: Champs-Elisees for shopping, Trocadero for perfect Tour Eiffel views, Les Halles and Chatelet for more shopping and Cite for Notre-Dame and just exploring the best part of Paris (including Le Marais), Montparnasse for the best city view, Chateau Rouge for Sacré-Cœur and another great city view from its dome plus Moulin Rouge and more.
Welcome wine was a nice touch, we really appreciated it late in the evening after 14 hours travel :)