Sylvie's apartment is lovely. Being relatively central and three minutes from the Metro means it's easy to get to and the local amenties are good (there's a large Monoprix a few minutes down the street and a good selection of bars and restaurants just minutes away (the Lebanese restaurant is worth visiting and the Thai restaurant looked good).
You get to Sylvie's apartment through a courtyard (which seemed very Parisian) and is on the second floor. The stairs are not good for vertigo sufferers (i.e. my wife) but manageable. And the flat is fantastic. As you walk through the door you're presented with art on much of the available wall space (the fridge has an amazing collection of fridge magnets depicting 20th century art) - if you like stark white walls and minimalist decoration, this is not the place for you.
The apartment had everything we needed and there was plenty of space for the three of us to relax. The kitchen was well stocked, both in terms of utensils and basic (and not-so-basic) items (tea, coffee, sugar, oil etc. and an array of herbs and spices and those bits you always miss when trying to cook away from home).
Neither bedroom is enormous but the beds are comfortable. One wall of the apartment is mostly windows, so it catches the sun and generally light, but there are excellent blinds and the windows all open so we weren't too hot even though it was rather warm outside.
Sylvie wasn't in Paris while we were there but her friend Pierre sorted everything out and was very friendly and welcoming. We had to get in touch with him about a couple of minor things and he was very quick to respond and always helpful.
We had an absolutely lovely stay in Paris, and Sylvie's apartment was a major factor in that. When you're exploring a city it's important to have somewhere you can relax after a hard day seeing amazing sights (our nine year old insisted we climb the Eiffel Tower, which was wonderful - the view from the top is breath-taking - but I was unsurprising tired that evening!), and Sylvie's apartment couldn't have been better for that. As we were leaving we all agreed we wanted to visit again!