I was in Greg´s place in early June2013. It is so much prettier than it looks in the pictures! It is really cool and absolutely tasteful. Besides that, as an experienced airbnb user I have to say it is one of the cleaniest I have been to. The decoration, the lighting is a big WOW. The kitchen is amazing, very large for a rental place. Every detail is taken care of: fresh flowers, sodas and coffee available, soap, shampoo. You can tell he takes it seriously and he devotes the amount of time (and money!) required to make a good impression.
As of the area it is very safe, 2 blocks away from metro station, easy to get to and full of small stores of all kinds in the area. Boston/Cambridge area is not very big, so it doesn´t take over 15 minutes to get to the heart of Boston. In my opinion the area is also so much nicer than it looks in the pictures!
Concerning the host, he was diligent to make sure we made it to the place with no inconveniences, he called me several times until he made sure we had made it there, he kept contact and was a fast answerer of our messages. His instructions on how to get there were specific and accurate and he was a very nice and well educated person.
The only thing to keep in mind is that it might not be suitable for old people or people with mobility problems, since it is on the first floor by stairs (by the way, the building itself is nice and clean too)
I am giving him the highest rating because both him and the place deserve it and I would certainly enjoy staying there again.