It was our first stay with airbnb and it was lovely staying with Carolina & Laura in Florence. We had a private room with shared bathroom. All was very nice and clean. There were books available if you don't have any reading material with you, maps of Florence and even a Lonely Planet guide of Italy.
You do have to climb up 76 stairs to reach this apartment :) I imagine it could be difficult with a heavy luggage.
It's very close to everything - perfect location, lots of bars, restaurants and shops around - not to mention top attractions in Florence - and just around the corner you can shop Gucci, Armani, stuff like that.