We stayed for 3 weeks in Caroline's lovely, well furnished apartment, and what a great stay it was! Situated in a very calm district (4th), it is meters away from the Belvedere, and 15 min walk to the city center. There are a few excellent and typical restaurants on the doorstep (you have to try the Salm Bräu!)
Communication was excellent, very friendly and quick. Unfortunately we didn't get to meet Caroline, but her friend Paul greeted us, he was friendly and warm.
We definitely recommend Caroline's place, for a short or long stay.