I had a great stay at Greg's place in the Latin Quarter of Paris. The location is very good, close to both the quaint, hip streets near the Sorbonne (e.g. Rue Mouffetard) and also close to the upscale area of Saint-Germain-des-Pres (6th arrondissement). It is an easy walk to the Pantheon and Jardin du Luxembourg, and if you're up for a longer but still manageable walk you can reach Notre Dame, Musee d'Orsay, Louvre, and Pompidou Center on foot as well. If you'd rather take the metro, which was surprisingly convenient and easy to use, there is a stop on Greg's street not even a block away.
The apartment itself is a very cool 19th Century apartment in one of the historic buildings that have made Paris's boulevards famous. Of course, it has a few quirks which any apartment of this age would have: small kitchen, toilet in separate room than sink and shower, creaky floors, etc. But I did not mind any of this-it's what gives it its charm, afterall, and the space is very clean and tidy. My bedroom had nice big windows which opened on to a long balcony which you can step right out onto, so plenty of fresh air and great views, too.
Although Greg was there while I was, he made it clear to me that I could come and go as I pleased, and we only crossed paths a few times. Even though I spent most of my days and nights out in the city, when I was home it felt mostly like I was alone in the apartment. He gave me use of the kitchen and dining area, and there are a few times I walked to a market less than a block away to bring food back to the apartment.
There is a faint smell of cigarette smoke as Greg does smoke in the apartment, so if you're hyper-sensitive to this then you should take note. I don't smoke but it was faint enough that I wasn't bothered by it. Also, the bed is small (twin), so if you're a couple you might want to note that as well.
Greg is very friendly and will give you recommendations/tips if you need them. All in all a great stay, great value for the money, and I would absolutely stay with Greg again. It felt like an authentic Paris experience!