We stayed at Guillaume et Penelope's apartment in late November and it was fantastic. It was super easy to communicate and we received frequent notes from their greeter, Samy, leading up to our stay. Getting into the apartment was easy and the place is NICE! The apartment is on the second floor (for Americans) and there is an elevator to bring up your luggage ... we used the stairs for the rest of the time.
The apartment is quite large compared to other places in Paris, the ceilings are about 15 feet tall, and it felt very private even with huge windows throughout. The bathroom is very modern with a great waterfall shower (plus wand) and two sinks. The bed was very comfortable and so was the couch (I got sick one night and slept out there). Best of all ... it was VERY CLEAN, which was important to my wife LOL.
The neighborhood is so close to everything and we walked to all the major sites with ease. Restaurants galore are nearby.
We recommend staying here and will do so again!