We booked the house for Xmas holiays 2013, we're a bunch of 5 people from Italy.
Location is amazing, very close to Union Square and the metro, basically you can go everywhere from here. The street is quiet and the brownstone building is really great, it gives you that feeling of being a "Newyorker" rather tahn simply a tourist.
The house is huge and with lots of character, it's on 3 levels plus there's an art studio in the attic. It's a real house where Joanna lives, so you really get the feeling of being in your home and not on holiday. There are tons of objects and arts (mostly paintings) everywhere, it's also possible to visit the art studio, if you love arts, you definitely have to pay a visit, it's definitely interesting.
Joanna is a great host, always replying to every e-mail and message. We had a huge delay with our flight, due to bad weather in Europe, and she was so kind to wait for us until late night, even if she had to leave for the countryside. She also helped us to stop 2 taxis in the street to get to the airport on our last day, very kind of her!
On the negative sides, being a huge and very old house, full of tons of personal objects, books and arts, it's also dusty and cleanliness is not up to Italian standards, but, then again it's an historic brownstone building not a new built house, so we were expecting something like that.
A tip for Italian people only, beware that, as usual in foreign countries, there's no bidet in the bathrooms!