I stayed with my girlfriend at Karen & Raffaele in December 2014, and have to say it was one of the most pleasant travel experiences i ever had. The flat is located in the historical center (few minutes by foot to Duomo) and the neighborhood has a lot of great restaurants. The flat itself is very cool, modern and artsy. The terrace is absolutely stunning, especially if it is sunny. Karen and Raffaele were really helpful since we came to Florence, they let us use their parking space as we have arrived by car, and recommended us great nearby places (not too touristy). They provided us with all the cooking equipment (even though we don't cook) but you can make yourself a cool breakfast and coffee. Definitely one of the most friendly people I had the chance to meet during our travel over Airbnb. Will stay there again next time when I am in Florence.
Thanks for the great time!